Synthesis of a crystalline form of tartrate salt of N- (4-fluorobenzyl) -N- (1-methylpiperidin-4-yl) -N '- (4- (2-methylpropyloxy) phenylmethyl) carbamide

A method for preparing a crystalline form hemitartrate N- (4-fluorobenzyl) -N- (1- methylpiperidin-4-yl) -N '- (4- (2-methylpropyloxy) phenylmethyl) carbamide of formula IV * * ** Formula (a) exhibits an endothermic signal at 177 ° C as measured by differential scanning calorimetry with a melting enthalpy of about 129 J / g; or (b) exhibits a diffraction pattern in X-ray powder comprising peaks having d-values ​​in angstroms of about 12.0, about 10.7, about 5.86, about 4.84, about 4.70, about 4.57 and approximately 3.77, wherein the method comprises; suspend a solid form of a compound of formula IV in an aprotic solvent, wherein the aprotic solvent is methyl ethyl ketone, stirring the suspension while seed crystals of the crystalline form having the signal by differential scanning calorimetry are added or the diffraction pattern in X-ray powder specified above, and isolating the crystalline form of the suspension.