Crystalline forms phosgene

Solid phosgene exists in three crystalline forms, identified by the following melting temperatures and calorimetrically-determined enthalpies of fusion solid I, T, = 145.37 K ... 

A solution of 32 g (030 mol) phosgene in 200 ml benzene is added dropwise at 30°C to a stirred soiution of 53.5 g (032 mol) 3-o-toloxy-13-Pfopanediol in 400 ml benzene. The mixture is stirred for an hour after the addition is completed, and a solution of 39 g of dl-methylaniline in 100 ml benzene is then added, and stirring continued for a half-hour. Ice water (about one-third volume) is then added, and the benzene layer formed is separated and stirred with 500 ml concentrated ammonia at 5°Cfor six hours. The precipitated solid (weighing about 55 g) is recovered and recrystallized from water. The product thus obtained in a yield of about 53 g is 3-(o-toloxy)-2-hydroxypropyl carbamate it is a crystalline solid melting at about 93°C, and having a lower water-solubility and higher oil-solubility than 3-o-toloxy-13-propanediol. 

A V -Carbonyldiimidazole (CDI) is prepared in a convenient and safe procedure from phosgene and imidazole as a non-toxic crystalline compound (m.p. 116-118 °C).[5],[6] It reacts almost quantitatively at room temperature or by short and moderate heating with an equimolar quantity of a carboxylic acid in tetrahydrofuran, chloroform, or similar inert solvents within a few minutes to give the corresponding carboxylic acid imidazolide, which is formed under release of carbon dioxide, together with one equivalent of readily separable and recyclable imidazole.Thus, this reaction leads under very mild conditions to the activation of a carboxylic acid appropriate for transacylation onto a nucleophile with an alcohol to an ester, with an amino compound to an amide or peptide, etc. 

Form Supplied in red solid prepared from optically pure d-camphor oxime in a five-step sequence (eq 1) reduction with sodium in n-amyl alcohol followed by fractional recrystallization of the resulting hydrochloride salts of bornylamines gives the endo-isomer in enantiomerically pure form treatment with phosgene and direct condensation of the isocyanate with (ethoxycarbonyl)hydrazine gives a compound which cyclizes upon treatment with base subsequent nitrogen dioxide oxidation furnishes (-)-en[Pg.145]

Phosgene reacts with pyridine forming a yellow crystalline substance of the formula C5HgN(Cl).CO.(C NCjHs, which is decomposed by water with formation of carbon dioxide according to the equation ... 

In practice, in order to detect phosgene mixed with air or other inert gas by this method, it is sufficient to bubble the gas mixture under test through a few ml. of water saturated with aniline in the cold (3 gm. aniline in 100 ml. water). A white crystalline precipitate forms which can be easily seen, and, if necessary, confirmed by microscopic examination (rhombic prisms) or by a determination of the melting point (236° C.). 

Crystalline l,r-carbonyldiimidazole 16, prepared from phosgene and imidazole, is particularly reactive. Even at room temperature, it reacts vigorously with water to give imidazole and carbon dioxide. With carboxylic acids in aprotic solvents, 1-acyloxycarbonylimidazole 17 is formed, which is capable of an intermolecular transacylation ... 

Analogous to amino acids, a-hydroxy acids form cyclic anhydrides when treated with phosgene. However, a much more efficient reagent for this transformation with lactic acid is trichloromethyl chloroformate. By this method, L-lactic acid O-carboxyanhydride (3) is prepared as a crystalline solid in 46% yield [2]. Although 3 has found application in polymer chemistry, its use in asymmetric synthesis has been limited. Reaction of 3 with 4-bromo-benzaldehyde methylthio(thiocarbonyl)hydrazone in the presence of TFA gives a mixture of 4 (25%) and 5 (56%), which is separable by column chromatography [3]. 

Phosgene oxime (dichloroformoxime) is a colorless crystalline solid with a melting point of approximately 37.7°C (100°F). In liquid or vapor form it is highly corrosive, and it penetrates clothing and mbber readily. The mechanism by which it damages tissue is unknown, but its effects are almost instantaneous and produce severe pain. Skin lesions are like those caused by a strong acid. There is no antidote treatment will be similar to that for mustard. 

By the aid of a modified peptide synthesizer solutions of two moles of Boc- or Ddz-amino acid salts (sodium- or triethylammonium form) in tetrahydrofuran or dichloro-methane at —40 °C are mixed for 5 minutes with one mole of phosgene in the same solvent at —40 °C, controlled by the punched tape program of the synthesizer (Fig. 44). The solution of the symmetric anhydride is added at —40 C to the gel polymer, which is contained in the centrifugal reactor (see p. 75) and is allowed to warm up to the cooling water temperature level (9—13 C) of the reactor during the peptide synthesis period of 30 minutes. Since the mode of action of the centrifugal reactor renders it possible to perfuse an external IR flow cell with the reaction solution, we are in a position to monitor directly the quality of the symmetric anhydride and its consumption, watching the characteristic absorptions on 1,830 and 1,760 cm [71]. In several cases the symmetric anhydrides were isolated in crystalline or solid form for characterization (Table 6). 

Typical procedure. Di-Dnp-carbonate 717 [503] To a stirred solution of phosgene (for a safe source, see Chapter 7) (178 g, 1.8 mol) in toluene (520 mL), dry sodium 4-nitrophenolate 876 (645 g, 4 mol) was added in portions from a flask attached by a rubber tube. The reaction flask was cooled during the addition to keep the temperature of the reaction mixture below 40 °C. Then, the mixture was heated by means of a water bath at 60 °C for 3 h. The precipitate formed was filtered off, washed with acetone (500 mL), and the combined filtrate and washings were concentrated to dryness. The crystalline residue was recrystallized from toluene, and then from CCI4 yield 428 g (78%) of 717 mp 140-141 °C IR (KBr) =... 

Crystallization of cis—1,4-polyisoprene from solution at -65 C has been carried out it is therefore possible that block copolymer preparation by epoxidation, bromination or some other reaction could be accomplished with lamellas of this polymer. Lamellar crystallization of cellulose, of amylose and of polyacrylic acid have been reported substitution reactions such as acetylation or ether formation with the hydroxyl groups and esterfication of the acid groups are possible reactions to carry out with lamellas of those polymers. The use of nonaqueous systems may be better suited to prevent swelling, and therefore, attack of the crystalline regions. It should also be possible to react poly(vinylalcohol) lamellas in suspension with acids or anhydrides to form vinyl-alcohol-vinyl ester block copolymers or with phosgene to obtain chloroformate groups which can undergo further reactions. 

In order to avoid the need for DCC, a number of activated derivatives of IV-hydroxysuccinimide itself have been developed which react directly with, for example, an oi-amino acid to provide the required activated oi-amino acid esters. These include the commercially available carbonate (1), a stable crystalline solid obtained from HOSu and Trichloromethyl Chloroformate or from 0-trimethylsilyloxysuccinimide and Phosgene and the related phosphate (2) derived from HOSu and Diphenyl Phosphorochlo-ridate under Schotten-Baumann conditions. Another alternative (also commercially available) is the oxalate (3), formed from HOSu and Oxalyl Chloride In general, these intermediates react rapidly with an iV -protected a-amino acid, usually in the presence of a mild base such as pyridine, to provide excellent yields of the required hydroxysuccinimide esters, generally with less racemization than is sometimes associated with the HOSu-DCC method. It is also possible to cany out the entire process of peptide synthesis in one pot using these reagents. 

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