Q.Identify A and B in the following reactions.
C6H5CH2Br --alco. KCN--> A --Na/ethanol--> B.

Amines are built by five general strategies, each testable by 'which reagent gives which amine class'. (1) FROM NITRO COMPOUNDS: H2/Ni (or Sn/HCl, Pd/H2) reduces a nitroalkane/nitroarene to a PRIMARY amine (nitroethane to ethanamine; nitrobenzene to aniline). (2) FROM NITRILES: H2/Ni (or LiAlH4, or Na/C2H5OH -- the Na/ethanol variant specifically called the MENDIUS REACTION) reduces a cyanide to a PRIMARY amine; reducing an ISOCYANIDE instead (Na(Hg)/C2H5OH) gives a SECONDARY amine. (3) FROM AMIDES: LiAlH4 reduces an amide to the amine (same carbon count); HOFMANN'S DEGRADATION instead treats an amide with Br2/KOH to give a primary amine with ONE CARBON FEWER than the parent amide -- this carbon-shortening is the diagnostic signature of Hofmann degradation. (4) FROM ALKYL HALIDES: the GABRIEL PHTHALIMIDE SYNTHESIS (phthalimide to potassium phthalimide to N-alkylphthalimide via SN2 with R-X to hydrolysis) gives a pure PRIMARY amine and CANNOT make aniline (aryl halides resist the SN2 step); HOFMANN'S AMMONOLYSIS (R-X + alcoholic NH3, sealed tube) instead gives a mixture of 1/2/3 degree amines plus quaternary salt (excess NH3 favours primary; excess R-X favours the quaternary salt; reactivity RI > RBr > RCl); a third route converts R-X to R-N3 (NaN3) then reduces with LiAlH4 to the primary amine; and chlorobenzene + alcoholic NH3/Cu2O/200C gives aniline directly. (5) AMMONOLYSIS OF HYDROXYL COMPOUNDS: alcohol vapour + NH3 over Al2O3 (or silica/WO3) at 400C gives a mixture of all three amine classes (Sabatier-Mailhe method); phenol + NH3/ZnCl2/300C gives aniline directly.