A stirred suspension of 12.6 grams 6-aminopenicillanic acid in 130 ml dry
alcohol-free chloroform was treated with 16 ml triethylamine and then with
13.8 grams of a solution of 2-ethoxy-1-naphthoyl chloride in 95 ml
chloroform. After being washed successively with 58 ml each of 1 N and then
0.1 N hydrochloric acid the chloroform solution was extracted with N aqueous
sodium bicarbonate (58 ml + 6 ml). The combined bicarbonate extracts were
washed with 20 ml ether and then evaporated at low temperature and
pressure to give the crude sodium salt of 2-ethoxy-1-naphthylpenicillin [also
called sodium 6-(2-ethoxy-1-naphthamido)penicillinate] as a yellow powder
(20.3 grams). This was dissolved in 20 ml water at 30°C and diluted with 180
ml n-butanol, also at 30°C, with stirring. Slow cooling to 0°C gave colorless
needles of the product.
