Patent GB-615521-A (GB)
Title: Improvements in acylations with enol esters
Filed: 1945-05-11
Abstract: 2-Acetoxyisoprene, obtained by reacting methyl isopropenyl ketone and isopropenyl acetate in the presence of p-toluene sulphonic acid as catalyst (see Group IV (b)) polymerizes rapidly on standing at room temperature.ALSO:Enol-esters of ketones are produced by acylating a ketone containing from 4 to 9 carbon atoms and having a hydrogen atom attached to an aliphatic carbon atom, either adjacent to the carbonyl group or joined to the carbonyl group by at least one pair of olefinically linked carbon atoms, by treating it, in the presence of an esterification catalyst, with an aliphatic carboxylic acid ester derived from an acid containing from 2 to 8 carbon atoms of the enol form of a ketone which contains from 3 to 9 carbon atoms and which is different from the ketone to be acylated.  The ester group of the acylating agent is transferred to the ketone to be acylated which thus becomes esterified in its enolic form while the residue of the acylating agent reverts to its ketone form.  Ketones which may be acylated include methyl ethyl ketone, methyl propyl (butyl, pentyl, hexyl or heptyl) ketones, diethyl ketone, ethyl propyl (butyl, pentyl or hexyl) ketones, dipropyl ketones, propyl butyl (or pentyl) ketones, dibutyl ketones, methyl cyclohexyl ketone, ethyl cyclohexyl ketone, cyclohexyl acetone, cyclohexanone, methyl cyclohexanones, ethyl (or propyl) cyclohexanones, acetophenone, tolyl methyl ketones, benzyl methyl ketone, acetyl acetone.  Ketones, the enol-esters of which may serve as acylating agents, include all the above and in addition, acetone, and specified enol-esters are those of acetic, propionic, butyric, pentanoic, hexanoic, heptanoic, octanoic, acrylic, crotonic, angelic, pentenoic or hexenoic acids.  The reaction may be conducted in the liquid or vapour phase and at normal atmospheric pressure or at higher or lower pressures.  The reaction temperature may be from 0 DEG  to 275 DEG  C. and preferably from 50 DEG  to 200 DEG  C.  Specified esterification catalysts are phosphoric acid, sulphuric acid and p-toluene sulphonic acid.  In examples: (1) a mixture of ethylidene acetone, isopropenyl acetate, cupric acetate and concentrated sulphuric acid is boiled in a still provided with a column packed with glass helices.  The acetone formed is removed by distillation and the remaining material fractionated to yield acetoxypentadiene which may be 2-acetoxypentadiene-1,3 or 2-acetoxypentadiene-2,4 or a mixture thereof; (2) cyclohexanone and isopropenyl acetate are reacted as in (1) in the presence of sulphuric acid to yield cyclohexenyl acetate; (3) alphaacetoxystyrene is obtained from isopropenyl acetate and acetophenone using sulphuric acid is catalyst, the acetone formed being removed by distillation; (4) methyl ethyl ketone is reacted with isopropenyl acetate in the presence of sulphuric acid to yield a mixture of 2-acetoxybutene-1 and 2-acetoxybutene-2; (5) 2-acetoxy-isoprene is obtained by reacting methyl isopropenyl ketone and isopropenyl acetate as in (1) in the presence of p-toluene sulphonic acid as catalyst, the product polymerizes rapidly on standing at room temperature; (6) a mixture of acetyl acetone, isopropenyl acetate and sulphuric acid is reacted as in (1), the acetone formed is removed by distillation, the reaction mixture neutralized with triamylamine and 2-keto-4-acetoxypentene-3 obtained by distillation under reduced pressure.  Enol-esters used as acylating agents in which the enolic form of the ketone is esterified with an acid other than acetic, may be prepared by reacting the enol acetate of the ketone with the anhydride of the acid in the presence of an esterification catalyst, thus isopropenyl butyrate and isopropenyl sorbate may be obtained by reacting isopropenyl acetate with butyric anhydride and sorbic anhydride respectively in the presence of sulphuric acid.  The Specification as open to inspection under Sect. 91 is not limited to the use of ketones containing a specified number of carbon atoms nor to esters derived from acids and enolic forms of ketones containing specified numbers of carbon atoms and as ketones which may be acylated or the enol-esters of which may be used as acylating agents the following are also specified: ethyl heptyl ketones, propyl hexyl ketones, butyl pentyl ketones, dipentyl ketones, propyl cyclohexyl ketones, butyl cyclohexanones.  The acylating agent may also be an ester derived from nonanoic, decanoic, lauric, palmitic, stearic, oleic, benzoic and hexahydrobenzoic acids. This subject-matter does not appear in the Specification as accepted.