| abstract |
Methods for preparing 3-methyl-2-buten-1-ol (prenyl alcohol) from 2-methyl-1,3-butadiene (isoprene) and carboxylic acids are disclosed. Carboxylic acids which can be used in the process have a K a (relative to water) greater than 10 -4 ; dichloroacetic acid is especially preferred. The process involves the slow (e.g., dropwise) addition of isoprene to the carboxylic acid to form a prenyl ester. The ester-formation reaction proceeds at room temperature in most cases; use of an organic base catalyst, preferably a sodium or potassium salt of the reactant carboxylic acid, improves the yield. The resultant prenyl ester can be converted to prenyl alcohol by reaction with a base. Prenyl alcohol can be readily converted to citral, a chemical intermediate in the synthesis of vitamins A and E, and several widely-used carotenoids. |