1,2,2,2-tetrachloroethyl chloroformate

Some interesting miscellaneous reactions have been also explored. For example, 1,2,2,2-tetrachloroethyl chloroformate reacts with carboxylic acids at 110°C without solvent to afford acid chlorides or cyclic anhydrides in high yields (Ref. 109). 

Scheme 84 Preparation of acid chlorides or anhydrides through reaction of 1,2,2,2-tetrachloroethyl chloroformate with carboxylic acids.

The facile preparation of 1,2,2,2-tetrachloroethyl chloroformate by treatment of chloral with phosgene in the presence of a reusable naked Cl- catalyst has been already described in section 3-2-2-3. We thought that if this chloroformate could be induced to undergo a Boord elimination of chlorine, the desired 2,2-dichlorovinyl chloroformate would be easily available as shown in scheme 114. 

Despite these strong omens of failure, the reaction was successfully performed (Ref. 165, 166). When zinc dust was added in small portions to a solution of 1,2,2,2-tetrachloroethyl chloroformate in THF at room temperature, dichlorovinyl chloroformate was isolated in 75% distilled yield. Initiation of the reaction after addition of the first portion of zinc is variable in time and no more zinc should be added until the first portion has been consumed to... 

I) was easily prepared in good yield from 1,2,2,2-tetrachloroethyl chloroformate and tert-butanol by a simple procedure. In a typical example, pyridine (1 eq.) was slowly added to a cooled (0°C) solution of t.butyl alcohol and 1,2,2,2-tetrachloroethyl chloroformate (1 eq. of each). After stirring for 4 h at 20°C, washing with water and evaporation of the solvent and recrystallization from hexane, (I) was obtained in 87% yield (mp. 70°C). 

Dichlorovinyl chloroformate 104, a stable and active acylating agent (e.g. for the protection of alcohols in acidic media) was prepared for the first time from 1,2,2,2-tetrachloroethyl chloroformate 103 (an a-chloroalkyl chloroformate synthesized by treatment of chloral 102 with phosgene in the presence of a reusable naked Cl catalyst) by dehalogenation with Zn dust [58]. 

Typical procedure. 1,2,2,2-Tetrachloroethyl chloroformate 103 [58] Freshly distilled chloral (4.4 g, 0.030 mol) was added (over 30 min) to a stirred refluxing solution (dry-ice Dewar condenser) of benzyl tri-n-butylammonium chloride (BTBAC) (10 g, 0.032 mol) in phosgene (for a safe source, see Chapter 7) (60 mL). After 1 h, the excess phosgene was removed through a series of five bubble traps (empty, H2SO4, empty, aqueous NaOH, NH4OH to hood exhaust) with the aid of an aspirator, and the 1,2,2,2-tetrachloroethyl chloroformate was isolated by distillation bp 76-79 °C/19 Torr, 47.7 g (65% yield). Note Unless 1,2,2,2-tetrachloroethyl chloroformate is completely free from the catalyst, it slowly reverts to the reactants. 

Mixed aryl and oximido tetrachloroethyl carbonates are crystalline and stable compounds easily obtained by reaction of tetrachloroethyl chloroformate with substituted phenols or N-hydroxy imides as shown in table 3-12. 

The compound Co[(sacac)2cn] is square-planar with a magnetic moment of 2.19 B.M. The red crystals dissolve readily in organic solvents such as dichlo-romethane, dichloroethane, tetrachloroethylene, chloroform, carbon tetrachloride, ether, acetone, and the lower-molecular-weight alcohols, but they are insoluble in water. The visible spectrum in C2H4CI2 exhibits a weak absorption at 980 nm (e = ca. 38) with more intense bandsat529,481,413, 346, 333, 300, and 255 nm (e = ca. lO -lO ). In addition, a lower energy band typical of square-planar cobalt(ll) complexes occurs at 1870 nm in tetrachloroethyl-... 

The crystalline 1,2,2,2-tetrachloroethyl fluorenyl methyl carbonate obtained in 98% yield (mp. 98-100°C) from 1,2,2,2-tetraethyl chloroformate and fluorene methanol proved to be suitable for the preparation of Fmoc-aminu acids in good to excellent yields (Ref. 0- j. 

Halogenated hydrocarbons = Hydrocarbons containing chlorine, bromine, iodine, fluorine (e.g., chloroform, trichloroethylene, tetrachloroethyl-ene, polychlorinated biphenyls). 

As part of a research program aimed at developing synthetic applications of 1-chloroalkyl chloroformates, 1,2,2,2-tetrachloroethyl-tert-butyl carbonate CN-916) 77A-was introduced as a simple and efficient reagent for the Boc-protection of amino acids, as shown in the scheme below [563-565]. 

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