GB855696A - Improvements in the preparation of 1-chloro-3-methylbutene-2 - Google Patents

Abstract

1-Chloro-3-methyl-butene-2 is obtained by forming a mixture of isoprene and aqueous hydrochloric acid, homogenizing the mixture, subsequently allowing the mixture to separate into two layers, and then separating the organic layer containing 1-chloro-3-methyl-butene-2. The formation of the mixture is usually carried out over a period of 1 to 2 hours and the homogenization is generally effected by stirring, e.g. for 1 to 4 hours. An inert dispersing agent may be added to assist in the homogenization. Preferred temperatures for the formation of the mixture and the homogenization are 0 to 40 DEG C. and more preferably from 10 to 15 DEG C. It is preferred to use concentrated hydrochloric acid and preferably 2 to 3 moles of the concentrated acid are used for each mole of isoprene. The organic layer can be fractionally distilled to yield the pure product. A small amount of 3-chloro-3-methyl-butene-1 is also formed as by-product. An example is given. The crude or purified product can be condensed with sodium ethylacetoacetate to form isopentenylacetoacetic ethyl ester which can be saponified by bases and decarboxylated to methylheptenone (CH3)2 C=CHCH2 CH2 CO CH3). The latter product can also be obtained by condensing the crude or pure 1-chloro-3-methylbutene-2 product with acetone in the presence of an alkaline condensing agent, e.g. sodium hydroxide, potassium hydroxide, sodium amide or sodium alkoxide.