Preparation and Reactions of Certain Racemic and Optically Active Cyanohydrins Derived from 2-Chlorobenzaldehyde, 4-Fluorobenzaldehyde, Benzo[d][1,3]-dioxole-5-carbaldehyde and 2,3-Dihydrobenzo[b][1,4]dioxine-6-carbaldehyde. Antimicrobial and in vitro Antitumor Evaluation of the Products