The present invention relates to the preparation of mixtures of sterically hindered substituted N-secondary amino acids or their alkali metal salts by a one-step reductive condensation of an amino acid or its alkali metal salt containing a primary amino group and a ketone to thereby form a mono-substituted amino acid or alkali metal salt thereof, followed by preparing the corresponding sterically hindered tertiary amino acids or alkali metal salt thereof by reacting the mono-substituted amino acids or alkali metal salt thereof with an unhindered aldehyde under reducing conditions in the presence of a hydrogenating catalyst. The novel mixtures of the sterically hindered mono-substituted amino acids and the tertiary amino acids and their alkali metal salts are useful promoters for alkaline salts in "hot pot" acid gas scrubbing processes.