A method is disclosed for preparing a 2-substituted-5-oxo-3-pyrazolidinecarboxylate compound of Formula I. The method comprises contacting a succinic acid derivative of the formula R.sup.1OC(O)C(H)(X)C(R.sup.2a)(R.sup.2b)C(O)Y (i.e. Formula II)wherein X and Y are leaving groups and L, R.sup.1, R.sup.2a and R.sup.2b are as defined in the disclosure, with a substituted hydrazine of the formula LNHNH.sub.2 (i.e. Formula III) in the presence of a suitable acid scavenger and solvent. Also disclosed is the preparation of compounds of Formula IV wherein X.sup.1, R.sup.6, R.sup.7, R.sup.8a, R.sup.8b, R.sup.9, and n are as defined in the disclosure. Also disclosed is a composition comprising on a weight basis about 20 to 99% of the compound of Formula II wherein R.sup.1, R.sup.2a, R.sup.2b, R.sup.3, R.sup.4 and R.sup.5 are as defined in the disclosure; X is Cl, Br or I; and Y is F, Cl, Br or I; provided that when R.sup.2a and R.sup.2b are each H, and X and Y are each Cl then R.sup.1 is other than benzyl and when R.sup.2a and R.sup.2b are each phenyl, and X and Y are each Cl, then R.sup.1 is other than methyl or ethyl. Also disclosed is a crystalline composition comprising at least about 90% by weight of the compound of the formula R.sup.1OC(O)C(H)(X)C(R.sup.2a)(R.sup.2b)CO.sub.2H (i.e. Formula VI) wherein R.sup.2a and R.sup.2b are H, X is Br and R.sup.1 is methyl.