Final answer:
Peptide bond hydrolysis and Strecker synthesis can produce a free amino acid, while Gabriel synthesis normally uses phthalimide, which is excluded in the question.
Step-by-step explanation:
The processes that can produce a free amino acid are peptide bond hydrolysis, Strecker synthesis, and Gabriel synthesis. Peptide bond hydrolysis is a reaction where water is used to break a peptide bond in proteins, releasing free amino acids. Strecker synthesis is a series of chemical reactions that synthesizes an amino acid from an aldehyde or ketone, using ammonium chloride (as a source of ammonia) and potassium cyanide; this leads to the formation of an amino nitrile intermediate, which upon hydrolysis, gives a free amino acid. The Gabriel synthesis, traditionally involves phthalimide as a starting compound to generate a free amino acid, but the question explicitly excludes this method, hence, a Gabriel-style synthesis without phthalimide is not considered a standard approach and does not typically produce a free amino acid.