7Ferdinand Munx. Polyamino carboxylic acid and process of making same.[P]. Germany, US2130505, 1935.
8Roscoe Smith,J.L.Bullock,K.C.Bersworth,A.E.Martell, Carboxymethylation of amines. Ⅰ. Preparation of ethylenediamine tetraacetic acid [J]. J. Org. Chem., 1949, 14(3): 355-361.
9Frederick C, Bersworth, Vrona, N. J. Aliphatic polycarboxylic amino acids and processof making them.[P]. New Jersey, US2407645, 1946.
10Frederick C, Bersworth, Vrona, N. J. Method of producing carboxylic substituted aliphatic amines and metallic sals thereof.[P]. New Jersey, US2461519, 1949.
