A compound of the formula ##STR14## where X is S or O; R1, R2, R4 and R5 independently are hydrogen or lower alkyl of 1 to 3 carbons, and R3 is hydrogen or lower alkyl;A is lower branched chain alkyl having 2 to 6 carbons, cycloalkyl having 3 to 6 carbons, alkenyl having 2 to 6 carbons and 1 or 2 double bonds, alkynyl having 2 to 6 carbons and 1 or 2 triple bonds, (CH2)n and where n is an integer