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US Patent 2385303
Alkylation of Aromatic Compounds
This process is concerned with a method for mono-alkylating aromatic hydrocarbons by olefinic hydrocarbons using a Friedel-Crafts-type catalyst dissolved in a nitroparaffin to effect the reaction. Alkene-producing substances may also be used as a reactant, though generally under different reaction conditions from the alkene for which they would be used.
*all “parts” are by weight unless otherwise speficified
4 parts of AlCl3 dissolved in 5.7 parts of nitromethane formed a pale yellow solution to which 55 parts of benzene was added to form a light yellow solution. The last-named solution was placed in a reactor cooled to 0*C and 12 parts of propene was passed thereto over a period of 2.5 hours during which the reation temperature, because of exothermic heat of reaction, was allowed to increase to 40*C under 1 atm. The clear yellow product so obtained was washed with water, then with sufficient dilute sodium hydroxide to dissolve the precipitated aluminum hydroxide, finally dried and distilled to yield 20 parts of mono-isopropyl benzene, 8 parts di-isopropyl benzene and 2.5 parts of higher boiling material.
Similarly, 1 part of AlCl3 was dissolved in 2.3 parts of nitromethane and added to 80 parts benzene. This catalyzed the reaction with 15 parts of propene at 30-40*C to form 26 parts mono-isopropyl benzene, 10 parts di-isopropyl benzene and 5 parts of higher boiling material.
Only small amounts of ethylbenzene were obtained when ethylene was reacted with benzene as Example 1. Good yields were obtained at higher temperatures of 40-65*C under about 40 atm in the presence of HCl and AlCl3 dissolved in nitromethane. Thus a solution of 8 parts AlCl3 in 10 parts nitromethane and 80 parts benzene and 3 parts of HCl were mixed in an autoclave to which ethylene was added until a pressure of 40 atm was achieved. The reaction temperature was kept at 25*C for 1 hour and then increased to 40*C for 4 hours and finally to 65*C for 3 hours. The resulting product yielded 12 parts ethylbenzene and 6 parts of more highly-alkylated materials.
A solution containing 5 parts of AlCl3 dissolved in 5.7 parts of nitroethane mixed with 80 parts of benzene and propene was bubbled into the solution at 0*C and later at temperatures up to 40*C at 1 atm until 24 parts of propene had been added over three hours. The resulting products contained 31 parts isopropylbenzene, 16 parts di-isopropylbenzene and 7 parts of higher boiling material.
6 parts propene at 25 *C and 1 atm were added to a pre-made solution of 40parts benzene, 4 parts AlCl3 in 7.5 parts 2-nitropropane. The reaction products yielded 9.5 parts isopropylbenzene, 4.5 parts di-isopropylbenzene and 3 parts higher boiling material.
A clear yellow solution was formed using 10 parts anhydrous aluminum chloride and 15 parts 2-nitropropene. Upon addition of this solution to 80 parts benzene a clear red solution formed. No heat was evolved. The addition of 0.5 parts of di-isobutylene caused the red solution to turn yellow again. More alkene was added with shaking in portions of 5-10 parts until 32 parts was added at 1 atm. The reaction mixture was kept between 35-40*C with a cooled water bath. The resulting solution after washing and drying was found to contain [red]4.5 parts t-butylbenzene and 38 parts of higher boiling material.
There were more examples, but they had no significant changes from the examples above. (one did include an alkyl halide instead of an alkene, but that is well covered elsewhere.
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FC'ing w Allylic alcohols JChemSocPerTrans (1994)
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Synthesis of 1-Arylalk-2-enes and 1-Arylalkanes via Friedel-Crafts Alkylation with Allyic Alcohols Catalyzed by an Acidic Clay
Keith Smith* and Guy M. Pollaud
J.Chem.Soc Perkin Trans., 1, 3519-3520, (1994)
Moderately activated benzenoid compounds undergo alkylation with allylic compounds in the presence of acidic K10 clay to give almost exclusively 1-arylalk-2-enes by attack at the terminal position of the intermediate ally cation; catalytic hydrogenation yields the corresponding 1-arylalkanes.
1-Arylalkanes are important materials1 which are more viscous and more easily biodegradable than analogous 2- or 3-arylalkanes. Unfortunately, they are not usually available via direct Fridel-Crafts alkylation of aromatic substrates2 on account of the tendency of the primary carbocation intermediates to rearrange. Consequently, when they are needed in pure form they are generally prepared by Friedel-Crafts acylation followed by reduction of the ketone so produced to the hydrocarbon level. However, such procedures are too costly and too unfriendly towards the environment to be used for production of the bulk requirements of the detergents or lubricants industries, which therefore, continue to use mixtures consisting of 2-arylalkanes.
In recent years there have been many advances in the use of solid acid catalysts to control organic reactions.3-6 In accord with our own continuing interest in the use of solids for controlled organic synthesis5,7,8 we decided to investigate the possibility of using a solid acid to catalyze production of 1-arylalkanes via Friedel-Crafts alkylation and now report a novel, catalyzed alkylation of aromatic substrates with allylic alcohols which, in favorable cases, produces 1-arylalkenes selectively and in high yield. Such products are readily hydrogenated to give 1-arylalkanes.
Friedel-Crafts alkylations using alkenes as reagents are selectively catalyzed using a H-mordenite zeolite, but the major products are the corresponding 2-arylalkanes.9 We were not able to find a way of diverting the reaction to produce 1-arylalkanes. Attempted use of 1-haloalkanes as alkylating agents also led to only limited success, 32% of a 1-arylalkane being obtained with a 1-chloroalkane over dealuminated HY zeolite. Higher proportions of 1-arylalkanes than this have been claimed with conventional catalysts.10 We therefore turned our attention to allylic derivatives of types 1 and 2 in the hope that these would generate the stabilized allylic cation 3 and that this would react preferentially at its terminal position with aromatic substrates. Little work has been carried out using solid acid catalysts and allylic reagents of this type, but in homogeneous reactions protonic acids tend to catalyze reactions at the double bond while Lewis acids tend to catalyze allylic substitution.2b
3 R-CH-CH-CH2+ (resonance)
4 MeCH=CHCH2Ar (E)
In the presence of H-mordenite allylic chlorides 1 and 2 (R = Me, X = Cl) reacted with refluxing toluene to give reasonable yields of the terminally substituted product, 4. There was little evidence of further alkylation or of addition of hydrogen chloride to the double bond11 under the conditions used. Nevertheless, hydrogen chloride is not a favorable byproduct since it is corrosive, can damage the structure of the solid catalyst and can act as a competitive catalyst in its own right, leading perhaps to a different selection of products. Therefore, allylic alcohols were studied more extensively and 1 and 2 (R = pentyl, X = OH) were chosen as the test reagents (Scheme 1).
ArH + C5H11CH=CHCH2OH or C5H11CH(OH)CHCH2 –solid catalyst-> C5H11CH=CHCH2Ar + H2O
The efficiency of a number of different catalysts was tested under a standard set of reaction conditions (refluxing toluene solvent; 5 min reaction; mass ratio octenol: catalyst 1:0:3). The results are shown in Table 1.
Several important features emerge from Table 1. (i) There is little or no reaction under there conditions in the absence of a catalyst or with a soluble acid (methane sulfonic acid) catalyst. (ii) Several catalysts, notably silica, Amberlyst-15, H-ZSM-5 and H-X, bring about decomposition of the ocetenol without causing alkylation. (iii) The most acidic catalyst tried, H-Y with a silica:alumina ratio of 40, effectively catalyses the reaction buy also catalyses further reaction of the product 5, leading to lowering of the yield of 5. (iv) Fairly strong Bronsted acidic large-port zeolites and the acidic clay K10 are the most effective catalysts for the reaction. (v) The primary ocetenol produces somewhat higher yields than the secondary octenol, but both are effective reagents. Therefore, it is possible to use a mixture of the two.
In view of these findings, K10 was chosen for further investigation. The amount of catalyst could be reduced to a mass ratio of octenol:catalyst of ca. 1:0.05 by use of a longer reaction time (1hour), but the yield of 5 was a little lower. Drying of the K10 prior to use produced somewhat better yields. Zinc chloride supported on K1012 was not active as K10 alone. Therefore, K10 in high ratio was applied to a range of aromatic substrates. The results are given in Table 2.
Although it is likely that the optimal catalyst would be different for different substrates, with more acidic catalysts giving better results for deactivated substrates in accord with the comments relating to Table1, it is clear from the results in Table 2 that K10 can produce good yields of 1-arylalk-2-enes from a range of substrates of moderate activity. Furthermore, hydrogenation of compounds 5 according to Scheme 213 was straightforward and quantitative. Thus, the two-step sequence represented by Schemes 1 and 2 provides a new, high-yielding and convenient route to 1-arylalkanes (6). It should prove to be of considerable significance.
(5) C5H11CH=CHCH2Ar –H2 and Pd/C-> C5H11CH2CH2Ar (6)
We also note that solids which generally exhibit Bronsted acidity act to produce allylic substitution rather than addition to the double bond, in contrast to the reported situation with soluble acids.2b
Table 1: Efficiency of different catalystsa for reaction Scheme 1 (ArH = Toluene)
a Under standard conditions using catalyst (96mg) in toluene (7.5ml) at reflux and addition of octenol (320mg, 2.5mmol) in toluene (5ml) over a few minutes with stirring, followed by a further 5 minutes at reflux (see text).
b Determined from amount of octenol remaining (by GC).
c Determined by GC using an added standard.
d Products were characterized, following isolation by spinning band distillation of larger scale reaction mixtures, by NMR and MS and by conversion into arylalkanes by catalytic hydrogenation.
Table 2: Syntheses of products 5 according to Scheme 1 with K10 as catalyst (ratio alcohol:catalyst = 1:2; reaction time 5 min for each case)
(1) A. Davidsohn and B.M. Milwidsky, Synthetic Detergents, Wiley, New York, (1978).
(2) (a) G.A. Olah, Friedel-Crafts Chemistry, Wiley, New York, (1973);
(b) Marcel Dekker, New York, (1984);
(c) R. Taylor, Electrophilic Aromatic Substitution, Wiley, Chichester, (1990).
(3) P. Laszlo, Preparative Chemistry Using Supportive Reagents[I], Academic Press, London, (1987).
(4) W. Holderich, M. Hess and F. Naumann, [I]Angew. Chem., Int. Ed. Engl., (1988), 27, 226.
(5) K. Smith, Bull. Soc. Chim. Fr., (1989), 272, K. Smith, Organic Synthesis Using Solid Supports and Catalysts, Ellis Horwood, Chichester, (1992).
(6) H. van Bekkum, E.M. Flanigen and J.C. Jansen, Introduction to Zeolite Science and Practice, stud. Surf. Catal., (1991), 58.
(7) K. Smith, M. Butters, W.E. Paget and B. Nay, Synthesis, (1985), 1155; K. Smith, M. Butters, and B. Nay, Synthesis, (1985), 1157; Tetrahedron Lett., (1988), 29, 1319; A.G. Mistry, K.Smith, M.R. Bye Tetrahedron Lett., (1986), 27, 1051; K. Smith, D.M. James, A.G. Mistry, M.R. Bye, and
D.J. Faulkner, Tetrahedron, (1992), 48, 7479; K. Smith, D.M. James, I. Matthews and M.R. Bye, J. Chem. Soc. Perkin Trans. I, (1992), 1877.
(8) K. Smith, K. Fry, M. Butters and B. Nay, Tetrahedron Lett., (1989), 30, 5333; K. Smith and K. Fry, J. Chem. Soc., Chem. Commun., (1992), 187; K. Smith and D. Jones, J. Chem. Soc., Perkin Trans. I, (1992), 407.
(9) R.A. Grey, USP 4, 731, 479 (1988)
(10) S.H. Hsharman, JACS, (1962), 84, 2945.
(11) I. Mochida; K. Takeshita, M. Ohgai, and T. Seiyama, Ind. Eng. Chem.. Prod. Res. Dev., (1980), 19, 392.
(12) See, e.g., P. Laszlo and A. Mathy, Helv. Chim. Acta, (1987), 70, 577; J.H. Clark, A.P. Kybett, D.J. Macquarrie, S.J. Barlow and P. Landon, J. Chem. Soc. Chem. Commun., (1989), 1353; S.J. Barlow, J.H. Clark, M.R. Darby, A.P. Kybett, P. Landon, and K. Martin. J. Chem. Res., (S), (1991), 74.
(13) B.S. Furniss, A.J. Hannaford, P.W.G Smith and A.R. Tatchell, Vogel’s Textbook of Practical Organic Chemistry, Wiley, New York, (1989).
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Threads related to the Allyl-OH/K-10 clay FC alkylation above includes the following:
Post 103617 (Scooby Doo: "Alkylation of 1,3benzodioxole with K10", Chemistry Discourse)
Post 108727 (dormouse: "Allylpyrocatechol question -bloodgod100", Novel Discourse)
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