Characterization of asaraldehyde
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One of my 100.000 projects is related to the synthesis of asaraldehyde. One of the methods to identify asaraldehyde is MS, another NMR. However, most bees don't have these techniques at hand, or they can only dream of having access to these applications. Thank the Old Wise Men, we have several articles which might help us in the identification of a compound using much simpler methods. Determination of the melting point, for instance, is an often applied procedure. However, the mp of the pure substance is not always enough to be sure. That is where colour test and the synthesis of adducts pop in. An often used method is the formation of the semicarbazone. Here are some procedures to form some asaraldehyde adducts for the characterization of the product.
Rudolf Fabinyi, Tibor Szeki. Ueber einige Condensationsproducte des Asaraldehydes. Berichte der Deutschen chemischen Gesellschaft 39 (1906) 78
To our knowledge, there are 3 condensation products of asaraldehyde which have been characterized, viz the phenylhydrazone (J Russ phys-chem Gess 19, 3), the azine (Ber 32 (1899) 289) which has been synthesized by Buttlerow and Rizza, and Gattermann and Eggers to identify the aldehyde, and also the oxime (Z phys Chem 12, 578) which has been described by Fabinyi.
Asarum europeum can be found in large quantities in the woods surrounding Kolozsvar. In the early fall, we collected the roots and obtained a mixture of asarones via steam distillation. We used this opportunity to synthesize some asaraldehyde condensation products and to report our findings in this journal.
Synthesis of asaraldehyde
Buttlerow and Rizza (J Russ phys-chem Gess 19, 3) have described the synthesis of asaraldehyde for the first time, by oxidizing asarone with KMnO4 in carbonic acid. Much later, a method presented by Gattermann and Eggers (Berichte 32 (1899) 289) followed. Since we had a reasonable amount of asarone, we decided to follow the method of Buttlerow and Rizza, with this exception that we applied the KMnO4 oxidation in a sodium hydrogen carbonate solution. This results in a faster reaction, a cleaner product and a higher yield.
Procedure: a suspension of 15 g asarone in a solution of 40 g NaHCO3 in 600 mL boiling water was made, and a warm solution of 25 g KMnO4 in 400 mL water was added dropwise under strong stirring. The reaction mixture is filtered while it is still hot and asaraldehyde precipitates in the filtrate when it cools down. They form yellow needles, mp 114°C. Yield: 50-56%. By acidification of the filtrate, small quantities of the corresponding trimethoxy benzoic acid can be obtained.
A mixture of asaraldehyde and semicarbazide (from chlorohydrate and sodium acetate) is dissolved in alcohol. The semicarbazone precipitates as white crystals, the precipitation being completed in 24 hours. Recrystallization from alcohol yields snow-white, small needle-shaped crystals, mp 205-206°C.
Asaraldehyde and beta-naphtylamine are dissolved in alcohol. Soon, yellow flakes start to precipitate; they can be recrystallized from alcohol and melt at 134°C. Easily dissolved in ether and benzene.
The HCl salt, recrystallized from EtOH, builds rhombic crystals with blue tinting. Dissolving in water gives a yellow solution.
1 mol benzidine and 2 mol asaraldehyde are dissolved in alcohol and heated for several minutes. When the solution is allowed to cool down, very fine-build needles are formed. They don't dissolve well in ether and alcohol, better in benzene and very well in chloroform.
The hydrochloric acid salt builds bordeaux-red, fine and small microcrystals, which can be recrystallized from diluted HCl.
Knorr (Ann Chem 238, 179) demonstrated that 1-phenyl-3-methyl-5-pyrazolon forms condensation products with aldehydes, yielding indigo-like substances with a yellow to red colour. Obviously, we were interested in testing this reaction for asaraldehyde. We found that asaraldehyde reaction easily with phenyl methyl pyrazolon in alcohol. The reaction proceeds both in the cold as when heated, although the latter reaction proceeds faster. The reaction yields nice looking, shiny, long orange-red needles which readily dissolve in EtOH and well in benzene and chloroform. Mp 230°C.
(Asarylydene-acetone: (MeO)3-Ph-CH=CH-CO-CH3) Aldehydes condense with acetone, as demonstrated by Claisen and Ponder (Ann Chem 223, 139), to yield substances of general formula R-CH=CH-CO-CH3. This is also the case for asaraldehyde.
Procedure: 2 g asaraldehyde and 0.8 g acetone are dissolved in 25 mL alcohol and while the reaction mixture is mixed and gently heated (40-50°C), 0.5 mL 40% aqueous sodium hydrate (?, "Natronhydrat") is added dropwise and allowed to react for 24 h (warm, not hot). The now yellow reaction mixture is diluted with water and mixed.
Orange-yellow flakes precipitate and are recrystallized from hot alcohol; they melt at 173°C. They do hardly dissolve in ether, readily in acetone, GAA, boiling benzene and very well in chloroform. They colour cherryred with concentrated sulfuric acid.
A solution of the substance in chloroform colours green-blue when bromine is added; upon the addition of more bromine, the reaction mixture's colour becomes yellow again.[...]
Harries and Mueller (Ber 35 (1902) 966) found that benzaldehyde condensed with ethylmethylketone in the presence of diluted NaOH, to yield alpha-benzalmethylethylketone. A similar reaction for asaraldehyde can be postulated.
2 g asaraldehyde and 1 g ethylmethylketone are heated in 25 mL alcohol; 2 mL 40% NaOH is added. After 24 hours, another 2 mL NaOH is added and the reaction mixture mixed well. After several hours, yellow crystals precipitate. Several recrystallizations from alcohol yields crystals which melt at 155°C. They are hardly soluble in ether, readily in alcohol, acetone, benzene, GAA and very well in chloroform. Addition of bromine to the latter gives an intensely red coloured solution. A resinous product is obtained when te product is treated with bromine in CS2.
Similar method: 2 g asaraldehyde and 1 g methylpropylketone in alcohol with 40% NaOH. Recrystallization from alcohol of the precipitated product yields needles, mp 87°C. High solubility in chloroform.
2 g asaraldehyde and 2.5 g acetophenone are dissolved in 20 g alcohol and heated for 1/4 h at 60-65°C after addition of 10 g 40% NaOH. The reaction mixture will solidify on standing, yielding a white jelly of crystals. The trimethoxybenzal-bisacetophenone is crystallized from alcohol as white, fine needles, mp 119-120°C.
The oxime of asaryl-bisacetophenone builds white needles as well; they dissolve well in alcohol or GAA. Mp 167-168°C.
I guess these were the most important parts of the article. Other methods were formation of alpha-trimethoxyphenyl-beta-naphtocincho
Voila, hope it can be of use to somebody, who want to experiment with TMA-2 and feels the need to characterize his products but has no access to artsy-fartsy equipment .
Maybe I should add that I haven't tested these procedures yet (I just came back from my multi-mile walk to the library), but I have the intention to test at least some of them in the near future. We'll see...
The faster you run, the quicker you die.