(Hive Bee)
02-25-03 21:08
No 411522
      optimized OTC hydrazine sulfate synth
(Rated as: excellent)

I cannot claim credit for the following information. It was e-mailed to me by somebody who wishes to remain anonymous; see http://www.sciencemadness.org/talk/viewthread.php?tid=470. Most of his writings are not pertinent or appropriate to the Hive.

There are other Hive posts about hydrazine sulfate from urea and hypochlorite, but none so detailed.

The hydrazine sulfate synthesis which I have done successfully many times is a slightly modified procedure based on the method described by GB392845. Everything is OTC ingredient optimized and the yields are high, the hydrazine is freebased into methanol by a modified procedure similar to GB876038. This results in hydrazine hydrate in methanol. However, if the methanol contains sufficient sodium methoxide or potassium methoxide, by methods such as US2278550 or US4267396, then anhydrous hydrazine in methanol is the result :-). Good yields of alkali azides may be obtained by reaction of the methanolic hydrazine with isopropyl nitrite. See US1628380, US5098597, US5208002. Small scale syntheses for alkali azides are favored by anhydrous methods in my experience.


There is no problem using OTC materials if you compensate the approach and adjust for total water, and keep to the molar proportions. I could write up the details for Hydrazine Sulfate OTC optimized quick and easy. The reaction is a bit complicated by foaming at a point, so a lot of empty space in the reaction vessel is required, as headroom for preventing overflows. This constraint places the yield limit to about 140 grams of hydrazine sulfate for a "pickle jar" sized reaction vessel. Actually I do the reaction in a 4 liter erlenmeyer equipped with a 4 liter foam overflow return reservoir. A 6 liter flat bottomed florence flask would be better. The oxidation of urea proceeds just fine in the cold and I prechill the basified hypochlorite to 10 below 0 degrees centigrade. Get it stirring with a large stirbar, and pour the warm urea/gelatine solution into the vortex of the mixture. I let the reaction proceed on its own gentle exotherm for about 1 and one half hours, and through to a point of 75 per cent subsiding of foaming, before applying any supplemental heating to finish the oxidation. The foaming can get wild when the heat is applied if the reaction has not proceeded far enough towards completion before the heating is applied. This synthesis goes through some interesting color changes which help to track the progress of the reaction towards completion.

About two minutes after pouring in the warm urea/gelatine solution the mixture changes from light yellowish green to white and the mixture foams to double its volume. After ten minutes the stiff foam begins to break free under the influence of the stirbar and slowly subsides while becoming more mobile and stirrable. After one hour the foam has subsided to about two thirds its initial highpoint. A slight orange color is noted. The foam continues to fall and then heat is applied very gradually, because just a small heating will kick the reaction back into a vigorous foaming, and this is when the overflow may occur. The idea is to just nudge the reaction rate a bit, and then let it proceed to run on its own energy again. The orange color will become very pronounced and darker at this stage of the reaction, as the foaming subsides nearly completely. At this point it is safe to increase the temperature rapidly up about 85 or 90 degrees centigrade to drive the reaction to completion. At the endpoint of the reaction the dark orange color will dissipate almost completely, and the solution color will suddenly fade to a very pale slight yellow tint, almost clear. When you see that color change, the reaction is complete. Peak the temperature, and then discontinue heating. Immediately remove the flask to a cool water bath.

Hydrazine Sulfate OTC optimized, Experimental:

1500 ml of 10 per cent sodium hypochlorite is placed into a 2 liter glass jar, lightly sealed with a lid, and placed into the freezer overnight to chill to 15 below 0 degrees centigrade. Into the prechilled 1500 ml of "liquid pool chlorinator" is dropped a stirbar and while stirring, 194 grams of fine prilled NaOH is added into the vortex at a rate as fast as it will dissolve and not accumulate on the bottom. Because of the exotherm, the addition must be done in two portions in order to prevent excessive warming and thermal decomposition of the hypochlorite. The first portion of the NaOH should be about 110 grams, and then the solution should be rechilled in the freezer to about 0 degrees centigrade before adding in the same manner the remaining 84 grams of NaOH. The basified hypochlorite is then returned to the freezer for keeping, and to rechill to 15 below 0 degrees centigrade for its use later in the hydrazine synthesis.

In a separate half liter jar having a lid, 132 grams of urea is dissolved in 70 ml of hot distilled water.

In yet another half liter jar having a lid, 1.8 (one and eight tenths gram) grams of gelatine is dissolved in 70 ml of hot distilled water.

Shaking of these containers will facilitate the solution, and supplemental warming of the containers in a hot water bath will also be required. After these warm solutions are prepared, and all solids are dissolved, the two solutions are combined just before use, and the combined solutions are kept standing in a bowl of warm water to mainatain everything in solution and prevent the mixture from congealing, which will occur if the mixture is allowed to cool.

A 4 liter Erlenmeyer flask is placed upon a stirrer hotplate and a three inch stirbar is placed in the flask. The heat remains off. Into the neck of the flask is placed a wide mouth plastic funnel of one gallon capacity, the neck of the funnel is enlarged with a bushing cut from a two inch length of one and five eighths OD, one and one quarter ID, tygon vinyl tubing, for a snug fit in the neck of the flask. The plastic funnel serves as an overflow reservoir and return path for any foaming which may exceed the capacity of the flask during the reaction.

The previously prepared, cold basified hypochlorite solution is poured into the flask and the stirrer started without any heating. The previously prepared, warm combined solution of urea and gelatine is poured through the funnel into the well stirred hypochlorite.

After a couple of minutes the reaction will initiate, and after fifteen minutes the foaming mixture will occupy twice the original volume, and the foam will temporarily be very rigid and motionless, but this will not persist for more than a few minutes. The foam will begin to very slowly disintegrate and stir down. The foam is viscous enough to cause uncoupling of the stirbar on the stirplate, at speed settings above 40 per cent, so it is better to have it stir successfully at a conservative setting.

About one hour after the reaction is begun, supplemental heat is applied, cautiously at first, because about ten minutes later a renewed episode of foaming will occur. This is a very transient and less viscous foaming which dissipates quickly. The onset of this foaming will be indicated by a dark orange color about the reaction mixture. When this episode of foaming occurs the reaction is nearing completion, and with increasing heating of the mixture to about 90 degrees centigrade, the reaction is complete at about one and one half hours from the beginning.

I do not even measure the temperature endpoint, but establish the endpoint by observing the color shift from orange to a very pale yellow, almost clear......very light tint to the solution. When the mixture has become hot enough, and all the foaming has subsided, the moisture will begin to reflux on the walls of the flask above the liquid and in the neck area of the flask. This happens when a mixture
is nearing the boiling point, which is plenty hot enough for this reaction. So when the refluxing moisture and color change have occured, the heating is stopped and the flask is removed to a cooling bath. After the mixture has cooled down, it is acidified by the dropwise addition of dilute sulfuric acid, with stirring, and using the same overflow funnel setup as before. 1100 ml of density 1.260 new battery electrolyte, which is 35 per cent sulfuric acid, is added at a rate of 3 or 4 drips per second to the stirred solution, and an exotherm is evident during the neutralization / acidification. The acidified mixture is cooled to about 10 to 15 degrees centigrade for precipitation of the hydrazine sulfate, and allowed to stand for several hours to complete the precipitation. Do not chill the mixture very cold or huge amounts of Glaubers Salt (hydrated sodium sulfate) will settle out along with the hydrazine sulfate.

The hydrazine sulfate is filtered and dried, yield is 159 grams.

In the previous communication about the usefulness of urea, I failed to mention a patent which shows the usefulness of urea in synthesis of methylamine. EP 0037862 discloses a high yield synthesis for methylamine nitrate. Also see GB1548827 for a closely related synthesis. It is my guess that paraformaldehyde would react with a diluted urea/ammonium nitrate eutectic. There was a mention of the nitrate process at the Hive, but no details or followup information was posted in the methylamine FAQ. Also see GB168333.


19th century digital boy
(Hive Bee)
06-07-03 23:22
No 438503
      further improvements part 1  Bookmark   

Mr. Anonymous is at it again. If you have the patience to read  this chapter of his novel you'll find a number of small but valuable improvements to his previous work on OTC hydrazine sulfate.
Part 1:

Hydrazine Sulfate from urea and pool chlorinator is a synthesis which has been previously described. From six recent experiments there has been discovered and proven several refinements providing significant improvement upon the original process first reported. The improved method is more economical, and produces a higher yield of better product. The revised proportions of ingredients and temperatures and reaction times are confirmed to better control the foaming of the reaction mixture. During the series of six experiments small modifications upon the earlier synthesis which is an OTC adaptation of GB392845 have been evaluated, and the experiments produced consistently good results for each run.

The changes involve a larger batch size, a heavier stirbar, higher initial reaction temperature, and use of HCl for neutralization of the basic sodium compounds, before using sulfuric acid to precipitate the hydrazine sulfate by a method that improves the yield and quality of the crystals. It has been discovered that it is useful in the neutralization stage to first use HCl equivalent to approximately the required amount for converting the theoretical amount of Na2CO3 reaction by-product to NaCl. Then the remaining portion of the neutralization / acidification is accomplished with a much reduced requirement of H2SO4 for producing the hydrazine sulfate. Using HCl for the bulk of the neutralization is more economical, and it also eliminates the contamination by hydrated sodium sulfate by-product which is produced at near saturation levels if the entire neutralization / acidification is done using only H2SO4. Using HCl for the main portion of the neutralization also considerably reduces the total exotherm during the neutralization. The crystalline form and density of the hydrazine sulfate produced by final acidification using diluted H2SO4 is improved, and it crystallizes out in better yield, when the acidified reaction mixture containing hydrazine sulfate is predominately a sodium chloride solution, instead of a mixed solution of sodium chloride also containing large amounts of sodium sulfate. Previously, solutions resulting from the entire neutralization / acidification done using only H2SO4, could not be cooled down very cold without contaminating the hydrazine sulfate precipitate with a hydrated sodium sulfate coprecipitate. Six syntheses using the new method have confirmed a purer end product is obtained by making use of HCl for the first portion of the neutralization, and then using diluted sulfuric acid to complete the neutralization / acidification which precipitates the desired hydrazine sulfate, consistently resulting in better formed crystals of improved density and purity.

These more dense and better quality hydrazine sulfate crystals perform much better in subsequent reactions where hydrazine is freebased from its sulfate, requiring only half the previously required amount of added water to create stirrable slurries with NaOH for methanol extraction of the freebase hydrazine hydrate. The more dense better formed crystals of hydrazine sulfate may be freebased to hydrazine hydrate by portionwise additions of solid NaOH, the water produced as a by-product of the freebasing being almost sufficient alone for creating a stirrable slurry capable of being extracted with methanol, taking up the hydrazine hydrate in methanol while leaving behind the sodium sulfate as an insoluble residue. In practice it has been found that only 10 to 12 ml of added water per mole of hydrazine sulfate is sufficient for the purpose of keeping the mixture in the form of a slurry able to be extracted easily by methanol in sequential portions which are decanted from the residue until the hydrazine has been effectively extracted from the insoluble residue of sodium sulfate crystals.  Reducing the added water requirement to this small amount in the freebasing of the hydrazine has eliminated the need for elaborate dehydration schemes using alkoxides to obtain acceptable yields of sodium azide directly from the much drier methanolic extract of hydrazine hydrate.

For the synthesis of sodium azide, methanolic hydrazine hydrate extract is further basified to slight excess of an equimolar amount of NaOH and treated in the cold with a slight equimolar excess of isopropyl nitrite (preferable), or equivalent of ethylene glycol dinitrite, to consistently produce sodium azide directly, in 65 per cent total yield based on the hydrazine sulfate used for the freebasing of hydrazine hydrate into methanol. The improved freebasing technique using reduced added water provides a useful yield of sodium azide by a process which involves no hazardous distillations of hydrazine or other added tasks for chemical elimination of excess water. Isopropyl nitrite was found to have a low transesterfication activity on contact with methanol in thecold, with cooling provided by immersing the azide production flask in an ordinary 0 degrees cold water bath containing chunks of ice. With this cooling the partial pressure of methyl nitrite from transesterfication of the isopropyl nitrite was sufficiently low that the back pressure provided by immersing a vent line from the closed apparatus to a depth of sixteen inches into a water filled carboy prevented any free boiling away of the organic nitrite from the reaction producing sodium azide, until the reaction was very near its endpoint.  After three hours reaction in the cold, the temperature was raised to boil away unreacted nitrite and the back pressure peak upon heating to drive the reaction to completion was raised to six feet of water, (about two and one half pounds per square inch of back pressure), maintained for fifteen minutes, before gradually reducing the back pressure to atmosphere and allowing complete boiling off of any unreacted nitrite. An alternate attempt to freebase hydrazine hydrate and use isopropanol for the extraction failed because of the stratification of the liquid portion into two layers, leaving much of the hydrazine hydrate in the heavier more aqueous layer unextracted by the isopropanol. Full details for the synthesis of sodium azide will be provided in a later communication. This digression simply describes why the improved synthesis of the hydrazine sulfate is of special interest for producing the hydrazine sulfate in better crystalline form by a method which improves its usefulness particularly as a precursor material for OTC sodium azide, or when the purpose will be to freebase the hydrazine and extract it with methanol for any other use.

After the HCl / H2SO4 sequenced acidification of the mixture which precipitates hydrazine sulfate, the supernatant sodium chloride solution is far below saturation so it can be chilled without worry for contaminating the hydrazine sulfate with sodium chloride, and this new method does not produce the occasional gelation problems of the earlier method when sodium sulfate / sodium chloride solutions containing gelatine are chilled. There is already indigenous NaCl present in the reaction system from the original manufacture of the sodium hypochlorite solution, as well as additional NaCl produced from the decomposition of the sodium hypochlorite in its reaction with urea, so it just makes sense to first cheaply convert the reaction by-product sodium carbonate to NaCl, and then make a final addition of dilute H2SO4 to precipitate the hydrazine sulfate. That theory has proven correct by the results of several variations of the example experiment detailed below. The best yield from this synthesis was 236 grams dry weight of pure sparkling white crystals of hydrazine sulfate, from a total reaction mixture volume after neutralization / acidification of 3250 ml. (72 grams of hydrazine sulfate per liter completed reaction mixture). The range of varying yields for six experiments was 221 grams to 236 grams. After several synthetic steps are completed, the conversion rate is a minimum 125 grams sodium azide from the chemical conversion of one gallon of 10 per cent sodium hypochlorite liquid pool chlorinator. The synthesis is cheap in terms of chemicals, but many hours of time and work are required for performing the various intermediate steps to get from feedstock materials to the desired end product sodium azide.

The volume of the foaming at the highest point in only one experiment did not overflow the capacity of the 4 liter Erlenmeyer flask, but did rise to just about one inch below the beginning of the straight section of the neck of the flask.  In the average of several experiments the peak height of the foaming did rise into the overflow funnel in amounts varying from 500ml to 1000ml exceeding the capacity of flask. Exactly why these variations occur in the peak volume is unknown, but is probably due to slight variations in the dynamics of the reaction related to small differences in temperature and also related to variations in the exact composition of the hypochlorite solution which changes from decomposition in storage as it sits on the shelf.  The reduced peak volume for the foaming mixture is not precisely constant. The peak volume of the reaction mixture can vary over a range of a liter depending upon slight variations in temperature and stirring efficiency and small variations in the measured ingredients. However, the average peak volume observed for several experiments has been reduced sufficiently to establish that a significantly increased batch size can be managed in a four liter Erlenmeyer flask without experiencing any troublesome messy overflows due to excessive foaming. Optimum yields have been obtained using the following proportions and generally it was found that for each one per cent deviation from the described quantities, a two to two and one half per cent reduction in yields resulted.  This optimization is derived from six experiments, so only a few variations were tested, and it may be possible to perfect the proportions or reaction conditions further, after charting the results of many more experiments. But the procedure described below has produced consistently good yields and smooth, predictable reactions for the several syntheses which were done in this particular study.

Anyone wishing to do a charted study of the efficiency of the reaction would want to look at the quantity of gelatine across the range of plus or minus a tenth gram above and below 2. 5 grams, the urea across a range of plus five grams from 180 grams, and the NaOH across a range of plus ten grams from 255, adjusting the neutralization equivalents for the HCl requirement accordingly. The effect of a small addition of epsom salt in solution up to say three grams does have a significant effect in the reaction by creating a colloidal dispersion of magnesium hydroxide, and the effect this produces is a marked slowing of the color change transition from orange to almost clear, increasing the time duration for the reaction but not improving yields. The inclusion of epsom salt or the use of ammonium hydroxide as solvent for the urea were both tried separately and in combination, in an effort to improve the yields, but negative results were produced. In the case of ammonia, the reaction produced a geyser of foam and lowered yields significantly.  The best procedure determined from the results of the series of six experiments is described as follows:


1892 ml to 1900 ml (one half gallon US ) of 10 per cent Sodium Hypochlorite liquid pool chlorinator was placed in a one gallon glass pickle jar and sealed with a threaded lid, placed into the freezer overnight to chill to 10 below 0 degrees centigrade. A three inch oval 60 gram stirbar was placed into the jar and to the rapidly stirred cold sodium hypochlorite was added 170 grams of solid fine prilled NaOH poured into the vortex over two minutes. Stirring is kept vigorous to dissolve suspended particles of NaOH and not allow
accumulation of solid material on the bottom. When all the NaOH was dissolved, the jar was resealed
and returned to the freezer to cool down again for several hours. When the solution was again freezing cold, an additional portion of 85 grams of solid NaOH was added as before, for a total of 255 grams of solid NaOH, that is two thirds of the total being added in the first portion, and one third in the second portion. When all of the NaOH is again dissolved, the basified sodium hypochlorite solution is sealed and returned to the freezer for keeping. It is very important not to allow the sodium hypochlorite to become warm during these solutions of added NaOH. If your freezer cannot chill the solution cold enough between additions of NaOH, then make smaller additions of NaOH in more than two steps in order to keep the sodium hypochlorite cold. There is a large exotherm produced by the solution of the NaOH, so the sodium hypochlorite must be very cold at the beginning of these additions of NaOH in order to absorb the exotherm without becoming warm, which would decompose the thermally unstable hypochlorite, and significantly reduce the yield of hydrazine.

It is common for NaOH to be packaged in a plastic bottle of 510 grams. This is precisely the amount which would correspond to a gallon of pool hypochlorite, or two batches of the size described here which can be done conveniently in a 4 liter Erlenmeyer flask.

In a one pint jar having a threaded lid is placed 182 grams of urea and 100 ml hot distilled water. In a second one pint jar having a threaded lid is placed 2. 5 grams (two and five tenths grams) of gelatine and 100 ml hot distilled water.

A hot water bath and occasional swirling of these containers will assist forming clear solutions. The two solutions are combined in one container before addition to the chilled hypochlorite solution. Any undissolved urea will dissolve in the combined quantity of water from the warm gelatine solution, aided by gentle warming and stirring of the combined solutions. There is no need to keep the combined urea / gelatine solutions warm after everything is dissolved. At this dilution the urea / gelatine mixture will not congeal even standing overnight so long as it is not subjected to cold temperatures.

19th century digital boy
(Hive Bee)
06-07-03 23:25
No 438504
      improvements part 2  Bookmark   

Part 2:

On a large stirrer hotplate is placed a 4 liter Erlenmeyer flask having a three inch oval stirbar of sixty grams weight. This weight of stirbar or larger is recommended to prevent uncoupling in the viscous foam which initially forms in the reaction, and for creating sufficient turbulence to break up and stir down the foam. A regular 3 inch by 1 / 2 inch octagon or polygon stirbar will uncouple at about 45 percent speed on the stirplate, but the heavier magnet in the larger 3 inch oval stirbar enables it to remain coupled up to about a 65 per cent speed on the stirplate, which results in much better stirring when a task like breaking up a viscous foam is required.

In the neck of the 4 liter flask is placed a one gallon plastic funnel whose stem is enlarged with a sleeve bushing cut from a two inch length of one and five eighths OD, one and one quarter ID, tygon vinyl tubing, for a snug fit in the neck of the flask. The plastic funnel serves as an overflow reservoir and return path for the foaming which usually exceeds the capacity of the flask during the reaction. The peak reaction volume can sometimes remain within the flask, perhaps one in five is the chance the foaming reaction will not rise into the overflow space of the funnel, but the overflow funnel will provide a useful added capacity which is more often going to be needed than the few occasions when it is not reached and partially filled by the peak volume of foaming reaction mixture. It creates a messy and hazardous spill if an overflow of a hydrazine containing mixture goes pouring over expensive equipment and contaminates a work area, so a cheap plastic safeguard against this risk is a good sensible precaution which should be followed without fail every time this hydrazine synthesis is performed. If a large plastic funnel is not on hand, it would likely be sufficient to use an empty three liter plastic soda bottle having its bottom end cut off with scissors, inverted and the neck of the soda bottle secured to the neck of the flask with a strip of two inch wide duct tape.  I have not tried this, but the foam temperature is mild enough that the thin plastic soda bottle taped to the flask should work fine used in this way as an improvised overflow / return vessel. A small plastic bowl could be placed in the open end of the soda bottle to exclude air and vent carbon dioxide escaping from the reaction mixture. The observation I have made is that the reaction should be started cold, but not too cold, or
the gentle exotherm of the reaction will not smoothly sustain itself as the reaction proceeds on its own.
The thermodynamic curve of the reaction seems to favor beginning the reaction in a synthesis of this quantity, with the hypochlorite solution at about 5 (five) to 8 (eight) degrees centigrade. The foam viscosity caused by the gelatine content is reduced at this above freezing temperature, so the foaming is easier to break up by rapid stirring, even though the initial reaction rate is slightly higher and more foam is being produced more rapidly. Since the reaction begins at a higher rate initially, it also occurs that the foaming stage tends to last for a shorter duration, therefore the foam begins to dissipate earlier, and the total reaction time from beginning to endpoint is reduced, with lower endpoint temperatures. Good yields were observed with a reaction endpoint temperature of only 85 degrees centigrade. The best yields will generally result if the reaction mixture is allowed to proceed for 25 minutes before supplemental heating is applied, unless the foam begins to dissipate and reduce in volume on its own at an earlier time. At any point where the peak height of the foaming reaction begins to fall on its own, then the supplemental heating should be immediately applied, and the heating begun at a twenty per cent level, ramped in like increments increasing every five minutes to drive the reaction to completion. No problems with heat induced surge foaming occurred when this approach was used. The reaction proceeds smoothly with no reaction lagging / surging problems observed.

A good way to estimate the correct pouring temperature for the basified hypochlorite is to remove the jar from the freezer and let it sit while the apparatus for the synthesis is being assembled. A layer of frost will form on the cold surface of the glass jar. The stirbar is placed into a four liter Erlenmeyer and the one gallon overflow funnel is inserted snugly into the neck of the flask, placed upon a large stirrer hotplate. Observe the jar and note the time when the frost finishes melting. About ten minutes after the frost finishes melting, the cold basified hypochlorite is at the right temperature for pouring through the overflow funnel into the flask. The stirrer should be started at about 40 per cent speed without any heating, and the combined urea / gelatine solution poured quickly all at once through the overflow funnel into the vortex. The stirring speed should be immediately raised to about 60 per cent. The funnel is covered with a plastic plate to provide a spatter shield and reduce exposure of the reaction mixture to air. The reaction initiates immediately and a white foam rises quickly to almost the full capacity of the flask. After about fifteen minutes, usually the foam begins to subside very slowly, and at twenty minutes the mixture is stirring more freely still with the level of the foam having diminished further. A gradual slowly darkening in color towards orange will be observed as the minutes pass and the flask may feel slightly warm to the touch. There will become visible an upwardly spiraling pattern of streaks in the foam from the action of the stirrer and the foam will gradually stratify into two layers as it breaks up and begins to dissipate. The upper layer of foam will show a more coarse texture to the bubbles and develop an open cell spongy appearance at the time when the foam is about to dissipate completely. At twenty-five minutes the volume of the mixture sometimes reduces to 3200 ml, and supplemental heating is applied at a setting of 20 percent in any case. At thirty minutes the volume of foam is down to 3100 ml, heating is increased to 40 per cent. At thirty-five minutes the volume of foam is reduced to 2900 ml, and heating is increased to 60 per cent. The color of the mixture is becoming a distinct orange. At forty to fifty minutes, the foam has subsided to a clear transparent dark orange solution. The stirring is reduced to 20 per cent in order to prevent vortex aeration and foaming caused by excessive stirring, and the heat kept at 80 per cent. Over the next ten minutes the orange color will gradually fade at a visible rate in the completing reaction. The color will fade to a pale yellow, very light ale colored, almost clear solution and this will indicate the endpoint of the reaction.  The reaction mixture is (preferably) heated an additional five minutes after color fade ceases or optionally may be heated until moisture is condensing on the inner walls of the flask in the neck area of the flask. The heating is discontinued.

Please note that the description given for time intervals and the behavior of the reaction at a particular time interval are a generalization, and each reaction proceeds with its own individual variations upon that general theme. There are a range of peak volumes achieved, and time associations may differ by a few minutes from one reaction to the next. These variations seem to have no adverse effect on the yield. The reaction may be complete at 55 minutes or it may require twenty or even thirty minutes longer for the next reaction which is attempted to duplicate the reaction just performed. And yet the yield may be identical for each run, in spite of the evident difference in the dynamics of the two runs. Go figure. The conclusion at which I have arrived about this anomaly is that the reaction is simply sensitive to small variables which are then amplified in the way the reaction responds, yet the general reaction proceeds well to produce consistently good results in spite of the reaction rate variations observed. The overflow funnel is removed and the flask is quickly stoppered to exclude air. Then the flask is removed from the hotplate stirrer, and placed into a pan of water to help speed the cooling of the contents. The flask should be stoppered, but occasionally during the first few minutes of cooling the stopper should be dislodged to allow for breaking the vacuum produced as the hot water vapors in the flask condense. If this vacuum break precaution is not performed, there is a risk of imploding an ordinary wall thickness Erlenmeyer flask. Do not leave the flask open to the air or the hot free hydrazine solution may be decomposed by excessive contact with the air. There can initially be transients of pressure from effervescing carbon dioxide, then vacuum from condensing vapors, so loosely stopper the flask and dislodge the stopper occasionally until the pressure variations stabilize while the mixture is cooling.

After the flask has cooled in the plain water bath for about thirty minutes, it is placed in an ice water bath for about an hour to further cool in preparation for the neutralization. The exotherm of the neutralization process to follow will cause the cool mixture to gradually heat up until it becomes hot again. Pre-cooling the reaction mixture will allow the exotherm of neutralization to be absorbed without the mixture becoming excessively hot or boiling from the heat of neutralization. Limiting the temperature this way helps control the fumes being evolved during the neutralization, and also results in a consistent size of crystals for the precipitate which forms at the same time peak temperature is being reached.

While the reaction mixture is cooling, measure out a quantity of 650ml of 31. 45 per cent HCl (thirty-one and forty-five hundredths per cent pool grade muriatic acid, 20 Degrees Baume) and place this 650 ml HCl in a suitable closed container and chill the pre-measured 650 ml of HCl in an ice bath or in the freezer, in advance of its use for the first part of the neutralization reaction.

Also prepare a diluted sulfuric acid solution as follows : Place 175 ml cold distilled water in a 500 ml Erlenmeyer flask and place the flask in a shallow pan of cold water. Slowly, (Caution Exothermic!) in four 50 ml portions add to the water a total of 200 ml of H2SO4 drain cleaner of 92. 5 per cent H2SO4 concentration, swirling the flask after each 50 ml portion is added. After the heat of dilution subsides for a few minutes, place this flask containing the diluted sulfuric acid in a separate ice water bath or freezer to cool it for later use in the final neutralization.

19th century digital boy
(Hive Bee)
06-07-03 23:29
No 438505
      improvements part 3  Bookmark   

Part 3:

When the reaction mixture has cooled, the flask is returned to the stirplate and the stirrer is started with no heating. To the rapidly stirred solution is added dropwise 650 ml of ice cold HCl 31. 45 per cent, at a drip rate of about 3 drops per second. Observe for any excessive foaming from the neutralization of carbonate, and reduce the drip rate temporarily to reduce any excessive foaming if necessary. Hydrazine is decomposed by air, and in order to reduce easy exposure to air through the open neck of the flask, I prefer to wind an inch wide strip of paper toweling above the tip of the addition funnel until the thickness of the strip of paper toweling has formed a snug fit, effecting a one hole stopper which is a loose seal between the neck of the flask and the funnel discharge tip. This allows the carbon dioxide produced during neutralization to escape, but prevents air from freely swirling downward into the flask where it would contact the hydrazine. About three paper towels thickness folded back over itself until an inch wide strip is formed makes a good winding for this packing.

After the HCl addition has been completed, the mixture will have become warm again from the exotherm of the conversion of the basic sodium compounds to sodium chloride. The valve on the addition funnel is closed, and into the addition funnel is placed the cold diluted sulfuric acid which has been previously prepared.

To the rapidly stirred mixture is added dropwise the diluted H2SO4 at a drip rate of two drops per second. Observe for any excessive foaming during the early part of this addition, as was done before with the frst stage of the neutralization, and reduce the drip rate if necessary to control any transients of excessive foaming.  Generally the neutralization is well behaved and goes smoothly. The addition of the first half of the diluted sulfuric acid will convert all of the freebase hydrazine which is present in the solution into the highly soluble dibasic hydrazine salt, which will remain in solution.  It is during the addition of the remaining second half of the diluted sulfuric acid that the super soluble dihydrazine sulfate is converted to the slightly soluble monohydrazine sulfate which is precipitated. Because the solution has become hot from the neutralization process completed earlier, a considerable amount of the monohydrazine sulfate being formed during the addition of the last half of the diluted sulfuric acid will be held in the hot solution which will super saturate with the monohydrazine sulfate being formed, and then at a point where about two thirds of the total sulfuric acid has been added, the hot super saturated solution will become cloudy and suddenly an avalanche precipitation of monhydrazine sulfate crystals will occur, continuing that precipitation of crystals to the end of the addition of the remaining third of the sulfuric acid. Knowing from observation that this is the manner in which the precipitation always occurs allows for the speed of the precipitation to be slowed for better crystal development in the hot solution. When about sixty per cent of the diluted sulfuric acid has been added, the solution clarity is closely observed and the instant that any turbidity or cloudiness is observed occurring, the drip rate of he sulfuric acid is reduced to a slow one drop per second into the vigorously stirred hot solution. The very slow final neutralization and continuing vigorous stirring of the slowly cooling mixture for one hour past the end of the addition, provides for a controlled growth of high purity and dense crystals of a desirable form.  The stirring is then discontinued and the flask is stoppered and placed into a cooling bath of melting ice overnight to complete the crystallization. Some effervescence of dissolved carbon dioxide will be observed coming from the solution and this is normal.

Loosely stopper the flask because the continuing evolution of dissolved CO2 will gradually develop sufficient pressure to eject the stopper and send it flying if the stopper is snug. A short length of string draped over the opening of the flask between the stopper and the inner surface of the glass will break the seal sufficiently to slowly vent away any pressure from the effervescing carbon dioxide.

After cooling overnight in an ice water bath, the mixture should be stirred up one final time to dislodge fine bubbles of carbon dioxide from the mass of crystals and to loosen any clumps of crystals for easier filtering. The stirbar is retrieved from the mixture and it is ready to filter. A 500 ml portion of the cold supernatant liquid should be decanted into a wash bottle for use in rinsing residual crystals from the flask onto the filter. Most of the liquid can be decanted from the mass of crystals and most of the wet slug of crystals will slide from the flask smoothly onto the filter, with a bit of firm bumping of the flask bottom edge with the heel of the palm of the hand. A stream of liquid from the wash bottle is used to dislodge and rinse residual crystals onto the filter. The drained but still wet crystals are flooded on the filter with about 150 ml of 70 per cent isopropyl alcohol and with a glass rod are stirred into a thick slurry with the alcohol. As this alcohol rinse drains through the filter, a final rinse with about 75 ml of anhydrous isopropyl alcohol is streamed in a spiral pattern onto the surface of the filter cake with a wash bottle. These alcohol rinses will get rid of most of the residual salt water from the reaction mixture which is initially held in the filtered cystal mass by capillary action. The alcohol rinsed crystals should be drained on the filter placed on a blotter to wick away excess liquid as much as possible and then air dried on a warm glass tray.

The yield of dried sparkling white crystals of hydrazine sulfate is 221 to 236
grams, about 60 per cent of theory based on sodium hypochlorite.  It is believed that the variation in yields is due for the most part to slight variations in the composition of the commercially available 10 per cent solution of sodium hypochlorite.  The solution is unstable in storage, so its analysis changes as it sits on the shelf and gradually deteriorates.  The yield of the synthesis varies according to the actual analysis of the feedstock sodium hypochlorite solution at the time it is used for the synthesis. There may also be slight variations in the commercial sodium hypochlorite solution analysis from lot to lot and slight variations in the analysis for the same product supplied from different manufacturers. The rate of decomposition for the sodium hypochlorite solution is greatly reduced when it is stored in a cool location. At the warm outdoor temperatures of summer days, the decomposition is accelerated, and after some passage of time the solution will decompose completely in storage.

19th century digital boy