The yield of tert.-butylmagnesium bromide in one of the smaller-sized runs was 33.1%. Under corresponding conditions the yield of tert.- butylmagnesium chloride was 49.71%. Earlier results by Gilman and McCracken under different conditions showed tert.-butylmagnesium bromide to be formed in a 20.6% yield. The maximum yield of tert.-butylmagnesium chloride obtained in the several experiments was 58%. In large-sized runs the yield is im- proved as is ...