Zinc Acetates as Efficient Catalysts for the Synthesis of Bis-isocyanate Precursors

Abstract

Anhydrous and hydrated zinc acetates were found to efficiently catalyze alkoxycarbonylation of the aromatic diamines 2,4-toluenediamine (2,4-TDA) and 4,4′-diphenylmethane diamine (4,4′-MDA) with diethyl and dimethyl carbonate, providing the desired bis-carbamates in yields from 93 to 98%. Driving these reactions to completion required temperatures of ca. 190 °C for 2,4-TDA and ca. 180 °C for 4,4′-MDA, and alkyl carbonate-to-substrate molar ratios of 25:1 to 30:1. Higher catalyst loadings were required for 2,4-TDA (2.5 mol %) than for 4,4′-MDA (1 mol %).

Zr-MOF-808@MCM-41 catalyzed phosgene-free synthesis of polyurethane precursors

“…Several homogeneous and heterogeneous catalytic systems have been developed for the N-carbamoylation of aromatic amines with DMC. Homogeneous catalysts are lead compounds, 5,6 zinc derivatives, [7][8][9][10][11][12][13][14][15] Yb(OTf)3 16 and organocatalysts. 17,18 Among these, Zn(OAc)2 often gives the best activity for aromatic dicarbamate synthesis.…”

Methyl N-phenyl carbamate synthesis over Zn/Al/Ce mixed oxide derived from hydrotalcite-like precursors

“…So far, various metal salts including Zn, 11,[19][20][21][22] Pb, 8,11 Sn, 23 Na, 24 etc. had been successfully employed as homogeneous catalysts for the synthesis of MPC and other carbamates.…”

Important Green Chemistry and Catalysis: Non‐phosgene Syntheses of Isocyanates – Thermal Cracking Way

“…Similarly, zinc acetate and its hydrated derivative also showed excellent efficiency and selectivity in the methoxycarbonylation of MDA with DMC. [26,30,31] 6 as a catalyst, regardless of the electronic properties of the substituents or the ring substitution pattern. [32] The general mechanism for the methoxycarbonylation between DMC and diamines was proposed for the basic catalytic system (Scheme 3).…”

“…Similarly, zinc acetate and its hydrated derivative also showed excellent efficiency and selectivity in the methoxycarbonylation of MDA with DMC. [26,30,31] With a 25∶1 molar ratio of DMC to MDA, a temperature of 180 ℃, and 1 mol% Zn(OAc) 2 •2H 2 O, the desired dicarbamate was formed in 97% yield. Besides, aromatic amine substrates consistently gave high yields (up to 98%) with DMC or DEC using Zn 4 O(OAc) 6 as a catalyst, regardless of the electronic properties of the substituents or the ring substitution pattern.…”