Give applications of cyanohydrins with acetaldehyde with suitable reactions. $OR$ Give following conversions by using acetaldehyde as starting material.
$(a)$ Lactic acid and acrylic acid
$(b)$ Alanine
$(c)$ $1$-amino propane-$2$-ol

(N/A) Applications of cyanohydrins:
$(a)$ Conversion of acetaldehyde to Lactic acid and Acrylic acid:
$CH_3CHO + HCN \rightarrow CH_3CH(OH)CN$ (Acetaldehyde cyanohydrin)
$CH_3CH(OH)CN + H_2O, H^+ \rightarrow CH_3CH(OH)COOH$ (Lactic acid)
$CH_3CH(OH)COOH \xrightarrow{H_2SO_4, \Delta} CH_2=CH-COOH$ (Acrylic acid)
$(b)$ Conversion of acetaldehyde to Alanine:
$CH_3CH(OH)CN + NH_3 \rightarrow CH_3CH(NH_2)CN$
$CH_3CH(NH_2)CN + H_2O, H^+ \rightarrow CH_3CH(NH_2)COOH$ (Alanine)
$(c)$ Conversion of acetaldehyde to $1$-amino propane-$2$-ol:
$CH_3CH(OH)CN \xrightarrow{LiAlH_4, 4H} CH_3CH(OH)CH_2NH_2$ ($1$-amino propane-$2$-ol)