Dialkyl oxalate

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. 

Dialkyl oxalates can be prepared by oxidative CO coupling in the presence of alcohols. The first reported example of the synthesis was in a PdCl2—CUCI2 redox system (30,31). 

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 dialkyl oxalate thus prepared is hydroly2ed to oxaUc acid and the corresponding alcohol. 

Dialkyl Oxalates. Oxalic acid gives various esters. Dialkyl esters, ROOC—COOR, are industrially useful, but monoalkyl esters. 

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. 

Using a Diester (a Dialkyl Oxalate) or Related Synthon... 

Hydrazinobenzimidazole derivative 336 was treated with oxocarboxylic acids to give a hydrazone 337 which underwent ring closure to the fused triazinone 338 <2000JME96, 2001JME316>. Reaction with dialkyl oxalate allowed the synthesis of the triazinedione derivative 339 <2001JME4359>. 

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]. 

Dialkyl Oxalates. Oxalic acid gives various esters, Dialkyl esters ROOC—COOR, are industrially useful, but monoalkyl esters, ROOC— COOH, are not The dialkyl esters are characterized by good solvent properties and serve as starting materials in the synthesis of many organic compounds, such as pharmaceuticals, agrochemicals, and fine chemicals (qv). Among die dieslers, dimethyl, diediyl. and di-n-butyloxalates are industrially important. 

Benzo[ ]thienylmagnesium bromide is said to react with dialkyl oxalates at 36-40° to give esters of 2-benzo[6]thienylglyoxalic acid, and at 110-115° to give esters of 2-benzo[6]thienylglycolic acid.898... 

The synthesis of dialkyl oxalates by oxycarbonylation of alcohols in the presence of a dehydrating agent and a Wacker catalyst was first reported by Fenton in 1968 (equation 177).378,449 As for the previous oxycarbonylations, the presence of water is a strong inhibitor of the reaction and favors the side-formation of C02 (equation 178). Dehydrating agents such as triethyl orthoformate or boric anhydride are necessary to prevent water formation and subsequent deactivation of the... 

Palladium-based catalysts can be used for the oxidative coupling of CO to dialkyl oxalates and/or carbonates (102-104), and sufficient information is... 

By oxidative carbonylation of lower aliphatic alcohols in the presence of oxygen or other suitable oxidants dialkyl carbonates and dialkyl oxalates are obtained, depending on the catalyst and the chosen reaction conditions (eqs. (10) and (11)). 

Oxidative Carbonylation of Aliphatic Alcohols Giving Dialkyl Oxalates... 

Dialkyl oxalates are of great interest as solvents, as C2 building blocks in fine chemicals synthesis and as intermediates in the manufacture of oxamide, which serves as a fertilizer mainly in the cultivation of rice. Hydrogenation of dimethyl oxalate was extensively studied at the beginning of the 1980s, when Ube (Japan) and Union Carbide searched jointly for an alternative route to the base chemical ethylene glycol, independent of natural mineral-oil resources [51, 70, 71]. 

The preparation of dialkyl oxalates by oxidative carbonylation of alcohols was first described by Fenton et al. in the early 1970s [72-74]. For example, the reaction can be carried out at a temperature around 125 °C and a pressure of about 70 bar in the presence of PdCl2 and iron or copper salts. Water is formed as a by-product and has to be removed from the reaction mixture by the addition of water-binding agents such as trialkyl orthoformates. Instead of oxygen benzo-quinone can also be used for the reoxidation of the catalyst system. Ammonia or amines seem to have a positive influence on selectivity and efficiency of the reae-tion. For some more examples, cf. [77-80, 117]. Mechanistic studies give some indication that alkoxycarbonylpalladium species occur as intermediates [52, 75, 76] (eq. (12)). 

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,... 

Frankland-Duppa reaction. Formation of a-hydroxycarboxylic esters by reaction of dialkyl oxalates with alkyl halides in the presence of zinc, or amalgamated zinc, and acid. 

Similarly, Matus and Fischer (100) heated l-alkyl-/3-carboline with an excess of dialkyl oxalate and synthesized canthin-5,6-dione derivatives in 20-65% yield (Scheme 4). Catalytic hydrogenation of TV -benzylcanthin-... 

An interesting way to make polymeric dispersions in liquid polyethers is the synthesis in situ of a polyamide by the polycondensation reaction between a dialkyl oxalate (for example, diethyl oxalate [91]) and a diamine, such as 1,6 hexamethylenediamine (reaction 6.28) ... 

Miscellaneous Alkylating Agents. Noller and Dutton have studied the trialkyl phosphates as alkylation agents. They found that ethers are formed by using one equivalent of the trialkyl phosphate per mole of phenol. The 5delds of the ether in Table 14-1 are based on the amount of the alkyl radical available and hence are a measure of the relative alkylating ability of the various sulfate or phosphate esters. Dialkyl oxalates and ethyl-6-bromosorbate have also been used to alkylate phenol [Pg.818]

---