Phosgene treatment

Lactone product 104 is now susceptible to reductive C-3 hydroxyl removal, providing an enol product 105 that can be converted to the ketone 106 upon silica gel treatment. C-l a-hydroxylation of compound 106 provides compound 107. Compound 108 is then produced via Red-Al reduction of 107 and subsequent formation of the cyclic carbonate upon phosgene treatment (Scheme 7-33). 

Dyes with a urea bridge,-HN-CO-NH-, are also obtained by phosgene treatment of aminoazo compounds. The so-called I-acid imide (7), resorcinol, and rn -phenylenediamine are also of importance. 

C. I. Direct Yellow 50, 29025 [3214-47-9] (26) is obtained, for example, by phosgene treatment of two equivalents of the aminoazo dye prepared from diazo-tized 2-aminonaphthalene-4,8-disulfonic acid coupled to w-toluidine. 

By mixing two different aminoazo compounds ANH2 and BNH2 and subsequent phosgene treatment, the asymmetrical diphenylurea direct dye 28 is obtained in addition to the two symmetrical members. 

There are a number of yellow substantive dyes synthesized by this principle. Example C. I. Direct Yellow 41, 29005 [8005-53-6] (29) is obtained by phosgene treatment of an equimolar mixture of bases A (sulfanilic acid— cresidine) and B (jt>-nitroaniline—> salicylic acid and reduction of the N02 group). The mixture additionally contains the two corresponding symmetrical dyes. 

Fig. 51 Preparation of dextran carbonates and carbamantes after phosgene treatment...

Niobium(V) oxide trichloride is a significant impurity in niobium(V) chloride, which is used for the preparation of niobium metal. Indeed oxygen impurities in the high-purity niobium produced in this way originate largely with NbOCl 3, and the feasibility of its removal by phosgene treatment has been examined between 380 and 450 C [223,224] ... 

The number average molecular weight of the polymer is increased 5-6 fold by this phosgene condensation treatment with some unreacted hydroxyl groups still available for further condensation pol3nnerization. Such an increase in molecular weight implies that the hydroxyl functionality of the macrodiol is >1.6, if it consists of a mixture of monofunctional and difunctional alcohols . That the saponified polymer does contain difunctional alcohols is confirmed by the fact that it may be converted to an insoluble gel by treatment with silicon tetrachloride no gel is obtained from phosgene treatment. 

Rea.ctlons, As with other tertiary alcohols, esterification with carboxyUc acids is difficult and esters are prepared with anhydrides (181), acid chlorides (182), or ketene (183). Carbamic esters may be prepared by treatment with an isocyanate (184) or with phosgene followed by ammonia or an amine (185). 

A variation of this method involves the conversion of the amine into the amine hydrochloride prior to treatment with phosgene. This method has the advantage of producing generally cleaner products by retarding the secondary reaction of the free amine with carbamoyl chloride. 

Acid Chloride Formation. Monoacid chlorides of maleic and fumaric acid are not known. Treatment of maleic anhydride or maleic acid with various reagents such as phosgene [75-44-5] (qv), phthaloyl chloride [88-95-9] phosphoms pentachloride [10026-13-8] or thionyl chloride [7719-09-7] gives 5,5-dichloro-2(5JT)furanone [133565-92-1] (4) (26). Similar conditions convert fumaric acid to fumaryl chloride [627-63-4] (5) (26,27). NoncycHc maleyl chloride [22542-53-6] (6) forms in 11% yield at 220°C in the reaction of one mole of maleic anhydride with six moles of carbon tetrachloride [56-23-5] over an activated carbon [7440-44-4] catalyst (28). 

Treatment of coal with chlorine or bromine results in addition and substitution reactions. At temperatures up to 600°C chlorinolysis produces carbon tetrachloride, phosgene, and thionyl chloride (73). Treatment with fluorine or chlorine trifluoride at atmospheric pressure and 300°C can produce large yields of Hquid products. 

Because of its bitter taste and water iasolubiUty, guaiacol has been chemically modified to improve its properties. Sulfonation provides a mixture of guaiacol-4- and 5-sulfonic acids which, as the potassium salts, is water-soluble, comparatively tasteless, but less active than guaiacol. Treatment of the sodium salt of guaiacol with phosgene provides guaiacol carbonate [553-17-1] (3) which also lacks the bitter taste of guaiacol, but is less water-soluble. 

By application of the Corey-Winter reaction,vicinal diols 1 can be converted into olefins 3. The key step is the cleavage of cyclic thionocarbonates 2 (1,3-dioxolanyl-2-thiones) upon treatment with trivalent phosphorus compounds. The required cyclic thionocarbonate 2 can be prepared from a 1,2-diol 1 and thio-phosgene 4 in the presence of 4-dimethylaminopyridine (DMtVP) ... 

Reaction of w-methylpiperazine with phosgene affords the carbamoyl chloride (170). Treatment of this intermediate with diethylamine affords the antiparasitic agent diethyl carbamazine (171)... 

Treatment of 2,6-dimethylaniline (121) with phosgene and triethylamine affords the corre-S]ionding isocyanate (122). Condensation of that reactive intermediate with N-isopropylpropyl-cne-1,3-diamine leads to formation of urea 123. This product, recainam (123), acts as membrane Stabilizing agent and thus exhibits both local anesthetic and antiarrhythmic activity [30]. 

The polyurethane foam used for home insulation uses methanediphenyl-diisoevanate (MDI) as monomer. The MD1 is prepared by acid-cataly/ed reaction of aniline with formaldehyde, followed by treatment w ith phosgene COCl2- Propose mechanisms for both steps. 

A carboxylic acid (not the salt) can be the nucleophile if F is present. Mesylates are readily displaced, for example, by benzoic acid/CsF. Dihalides have been converted to diesters by this method. A COOH group can be conveniently protected by reaction of its ion with a phenacyl bromide (ArCOCH2Br). The resulting ester is easily cleaved when desired with zinc and acetic acid. Dialkyl carbonates can be prepared without phosgene (see 10-21) by phase-transfer catalyzed treatment of primary alkyl halides with dry KHCO3 and K2C03- ... 

Anhydrides can be formed from certain carboxylic acid salts for example, by treatment of trimethylammonium carboxylates with phosgene ... 

Treatment of a chiral amine with phosgene is the cheapest way to prepare symmetrical ureas [29]. Nevertheless, due to the toxicity and reactivity of that reagent, it can advantageously be replaced by triphosgene [30] or l,l -carbonyldiimidazole [31-34] or other derivatives such as l,l -carbonyldi-2(lH)-pyridinone [35]. This procedure can be extended to thiophosgene (Scheme 1) and its thio-analogues, such as l,l -thiocarbonyldi-2(lH)-pyridinone to produce thioureas [36] chiral diamines can thus be transformed into the corresponding monoureas or monothioureas. 

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