Dialkyl oxalates processes

Many industrial processes have been employed for the manufacture of oxahc acid since it was first synthesized. The following processes are in use worldwide oxidation of carbohydrates, the ethylene glycol process, the propylene process, the diaLkyl oxalate process, and the sodium formate process. 

Nitric acid oxidation is used where carbohydrates, ethylene glycol, and propylene are the starting materials. The diaLkyl oxalate process is the newest, where diaLkyl oxalate is synthesized from carbon monoxide and alcohol, then hydrolyzed to oxahc acid. This process has been developed by UBE Industries in Japan as a CO coupling technology in the course of exploring C-1 chemistry. 

The sodium formate process is comprised of six steps (/) the manufacture of sodium formate from carbon monoxide and sodium hydroxide, (2) manufacture of sodium oxalate by thermal dehydrogenation of sodium formate at 360°C, (J) manufacture of calcium oxalate (slurry), (4) recovery of sodium hydroxide, (5) decomposition of calcium oxalate where gypsum is produced as a by-product, and (6) purification of cmde oxahc acid. This process is no longer economical in the leading industrial countries. UBE Industries (Japan), for instance, once employed this process, but has been operating the newest diaLkyl oxalate process since 1978. The sodium formate process is, however, still used in China. 

UBE Industries, Ltd. has improved the basic method (32—48). In the UBE process, dialkyl oxalate is prepared by oxidative CO coupling in the presence of alkyl nitrite and a palladium catalyst. 

The second and third reactions are economical, but the first is not. The second reaction is used in a process where HCN is oxidized to (CN)2 and hydrolyzed in the presence of a strong acid catalyst to give oxamide. The third reaction is employed in a newly developed process where diaLkyl oxalates are converted to oxamide by the ammonolysis reaction. This reaction easily proceeds without catalysts and quantitatively gives oxamide as a powder. 

In another process, a dialkyl a-methyldiglycolate (formed from an alkyl lactate and an alkyl monochloroacetate) is reacted with dialkyl oxalate in the presence of a sodium alkoxide and dimethylformamide. The reaction product is cyclized, alkylated, hydrolyzed, and decarboxylated [187]. 

Based on their alkyl nitrite technology, Ube developed their own new proeess for the manufacture of dialkyl oxalates by oxidative carbonylation of alcohols. This process is a two-step reaction, in which alkyl nitrite acts as an reoxidant for the palladium catalyst system, similarly to the situation in the preparation of dialkyl carbonates mentioned above. The published patent literature does not make it possible to give exact details about the Ube industrial plant in Yamaguchi, Japan, which has produced several thousands tons of dibutyl oxalate annually since 1978. The first step of the manufacturing process for dialkyl oxalates is the preparation of the gaseous alkyl nitrite from NO, oxygen, and... 

Similarly to the case of dimethyl carbonate, much work has been done to make dialkyl oxalates accessible by a heterogeneously catalyzed gas-phase process [77,... 

Industrial processes for dialkyl oxalate and dimethyl carbonate from CO, alcohol and oxygen catalyzed by Pd have been developed by Ube Industries in Japan [2]. 

Dialkyl oxalate esters can be synthesized by oxidative carbonylation catalyzed by palladium complexes with a cocatalyst in the presence of alcohol. The process of... 

In this section, we mainly present industrial production of dialkyl oxalates, dialkyl carbonates, and related processes developed by Ube Industries. 

The reaction has fairly strict solvent limitations. Polar aprotic solvents are required, the most usual being the dialkyl phthalates and ethylene glycol dimethyl ether. Other esters are also useful, but acetone, ethanol and halogenated hydrocarbons are much less effective. Some admixture of tert. butanol (up to about 5%) has little effect, but water and other alcohols reduce the quantum yield. It is interesting that the active site of firefly luciferase is known to be particularly hydrophobic. The mechanisms of the two reactions are rather similar in that both require a highly active ester (the adenylate in the case of the firefly). Attack by peroxide occurs in both cases (m mmolecular in the luciferin) and this process may require a non-aqueous environment for maximum efficiency. Some of the most efficient oxalates are listed in Table 2. 

---