Synthesis using phosgene

The only reports of directed synthesis of coordination complexes in ionic liquids are from oxo-exchange chemistry. Exposure of chloroaluminate ionic liquids to water results in the formation of a variety of aluminium oxo- and hydroxo-contain-ing species [4]. Dissolution of metals more oxophilic than aluminium will generate metal oxohalide species. FFussey et al. have used phosgene (COCI2) to deoxochlori-nate [NbOa5] - (Scheme 6.1-1) [5]. 

Fig. 5.2 Peptide synthesis using Leuchs anhydrides amino acid 1 (with residue Ri) is reacted with phosgene to give the Leuchs anhydride. This reacts with amino acid 2 (residue R2) to give the peptide carbamate. The dipeptide is obtained after cleavage of C02...

Much the most important polycarbonate in commercial terms is made from 2,2-di(4-hydroxyphenyl)propane, commonly known as bisphenol A. This polymer was discovered and developed by Farbenfabriken Bayer [92], The synthesis and properties of this and many other polycarbonates were described by Schnell in 1956 [93], The polymer became available in Germany in 1959, and was given the trade name Makrolon by Bayer (in the USA, Merlon from Mobay). General Electric (GE) independently developed a melt polymerisation route based on transesterification of a bisphenol with DPC [94], Their product, Lexan, entered the US market in 1960. The solution polymerisation route using phosgene has since been displaced by an interfacial polymerisation. 

The successful application of sulfanyl amines in the diastereoselective and enantioselective synthesis of as-3,4-disubstituted /3-sultams has been reported (Scheme 56). The protocol is based on the oxidation of the 1,2-aminothiols 178 with hydrogen peroxide and ammonium heptamolybdate. Chlorination of the resulting /3-aminosulfonic acids was achieved using phosgene. The /3-aminosulfonyl chlorides 179 obtained were cyclized under basic conditions and without epimerization to yield the t -3,4-disubstituted /3-sultams 180 (>96% de, ee) (Table 13) <2005S1807>. 

The interest in the synthesis of carbamate esters [12] remains very high owing to their wide utilization [13]. The synthesis of these compounds generally uses phosgene [14] or isocyanates [15] as starting material. These are toxic, harmful compounds and, therefore, it is of interest to discover new synthetic routes to carbamate esters involving the use of less noxious starting materials. 

Bromine compounds are much more expensive than chlorine compounds and, since the atomic weight of bromine is about twice that of chlorine, the halogen cost incurred in the use of bromine compounds as intermediates is likely to be at least an order of magnitude greater than the cost of the corresponding chlorine compound. Not least for this reason, the synthesis of phosgene from bromine-containing compounds is unlikely to be economically practical and are probably not worthy of development on a purely commercial basis. However, C-Br bonds are more readily cleaved than C-CI bonds, and bromide is readily oxidized back to bromine. 

The thermal dissociation of phosgene into carbon monoxide and elemental chlorine. Equation (8.2), is the reverse of the reaction used widely, either thermally, catalytically or photochemlcally promoted, for the synthesis of phosgene (see Section 5.1). Thus, much of the chemistry relevant to this Section has already been covered in Chapters 5 and 6. Much of the early work, both kinetic and thermodynamic, was marred by a lack of appreciation of the importance of high purity, and the fact that the system takes a very long time to come... 

Phosgene is widely used as a chemical intermediate for the production of isocyanates used in polyurethane foams and in the synthesis of pharmaceuticals and pesticides [55]. Processes using phosgene require specialized cylinder storage, environmental enclosures, pipelines, fixtures under negative pressure... 

Preparation (4, 94). Details for the preparation have been submitted to Organic Synthesis. The phosgenation of amides is general caution the reaction can be exothermic. With less reactive amides DMF can be used as catalyst. AU a-haloenamines are highly hygroscopic. 

Synthesis of Phosgene Phosgene (COCI2) is a toxic gas that is used in the manufacture of certain dyes, pharmaceuticals, and pesticides. Phosgene can be produced by the reaction between carbon monoxide and chlorine described by the equation CO(g) - - Cl2(g) COCl2(g). Initially 1.0000 mol CO and 1.0000 mol CI2 are introduced into a 10.00-L reaction vessel. When equilibrium is established, both of their molar concentrations are found to be 0.0086 mol/L. What is the molar concentration of phosgene at equilibrium What is Keq for the system ... 

On the industrial scale, carbon monoxide is used as a reducing agent in metallurgical operations, in the refining of metallic nickel, in the synthesis of phosgene, and in the synthesis of a wide variety of organic compounds. In the laboratory, it is used in the preparation of carbonyls and aromatic aldehydes. 

Jensen and coworkers studied phosgene synthesis using a micropacked-bed reactor [7]. A silicon reactor consisting of a 20 mm long, 625 (im wide and 300 pm deep reaction channel (volume 3.75 mL) was employed (Figure 11.2). In order to avoid corrosion by chlorine, the microchannels were coated with a thin sflicon dioidde film (5000.. A fixed bed of activated carbon catalyst (1.3 mg, 53-73 pm) supported on alumina particles ( 3mg, 53-71 pm) was placed inside the microchannel. Chlorine and CO were mixed and fed into the microchannel network. The exit stream could be analyzed on-line using a mass spectrometer. 

FIGURE 9.22. Alternate synthesis to polyurethanes without using phosgene. 

Scheme 10. New synthesis of urethane without using phosgene...

The most widely utilized method for the synthesis of isocyanates, the phosgenation of amines, uses phosgene as a reagent. 

A procedure for the synthesis of of 4,4 -diphenylmethane diisocyanate 264 using phosgene has been described [145],... 

A report of the synthesis of acid anhydrides using phosgene gas has also appeared in the literature [1040, 1041]. Nicotinic anhydride 1371 was prepared from nicotinic acid 1370 with phosgene in 87-93% yield, as described in a very detailed... 

In a new and efficient synthesis of guanosine, l-alkoxycarbonyl-3-arylmethylcarbo-diimides serve as essential reagents. They can be synthesized in excellent yields from thioureas using phosgene [1252]. l-Ethoxycarbonyl-3-benzylcarbodiimide 1695 has been prepared quantitatively from the corresponding thiourea 1694 within 1 h at 80 °C. 

Another method used to remove phosgene substitutes from the desired products is to destroy them with appropriate nucleophiles such as water or alcohols. This method can, of course, only be applied when the product is insensitive to these nucleophiles, as is the case for carbamates, carbonates, ureas, cyanides, isocyanides, and alkyl chlorides. Chloroformates, carbamoyl chlorides, isocyanates, acyl chlorides, N-carboxylic anhydrides, and carbodiimides, on the other hand, cannot be purified by this method. Consequently, a synthesis of these compounds using phosgene is worthy of consideration. 

Carafa M, Quaranta E (2009) Synthesis of organic carbamates without using phosgene carbonylation of amines with carbonic acid diesters. Mini-Rev Org Chem 6 168-183... 

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