Chloroform as reagent

Carbonyl dichloride can be taken similarly to form acid anhydrides (equation 31). Via a mixed anhydride and in the presence of triethylamine, it is possible to prepare symmetrical anhydrides in high yield. ° °° A variation provides ethyl chloroformate as reagent.In a first step the carboxylic acid is ethoxycarbonylated in the presence of triethylamine and then reacted with free caiiioxylic acid to form the acid anhydride (equation 32). As the intermediate can be isolated, this is a good method of forming mixed anhydrides.In addition it seems to be particularly suitable for functionalized carboxylic acids such as hydroxy acids." Polymer-bound chloroformates may be advantageous in some cases. " " ... 

Mixed Anhydride Coupling. This very popiilar method, involving the use of alkyl chloroformates as reagents to make anhydrides v/ith acylamino acids or acylpeptides, has been reinvestigated. Determann, Heuer, Pfaender and Reinartz o have shown that exposinre of the mixed anhydride... 

Trimethylsilyl trichloroacetate, K2CO3, 18-crown-6, 100-150°, 1-2 h, 80-90% yield.This reagent silylates phenols, thiols, carboxylic acids, acetylenes, urethanes, and /3-keto esters, producing CO2 and chloroform as byproducts. 

Using ethyl chloroformate as a reagent for C-8—N bond cleavage (Section II,A,4), synthesis of ( )-canadaline (272) from tetrahydroberberine (26) was independently achieved by Ronsch (40) and Hanaoka et al. (41,45). Bond-cleaved iodide 40a or chloride 40b was converted to the acetate 280 or the alcohol 281, both of which were easily derivatized to 272 through reduction of the urethane and oxidation of the alcohol 274 (Scheme 48). 

Mixed anhydrides (see Section 2.6) The mixed-anhydride method provides efficient coupling of peptides with minimal isomerization if the established protocol is strictly adhered to. This includes a short activation time at low temperature, isopropyl chloroformate as the reagent, and A-methylmorpho-line or /V-mcthylpipcridinc as the tertiary amine (Figure 2.25, path D). In what is an apparent anomaly with respect to conventional wisdom, a polar solvent such as dimethylformamide seems to be preferable to apolar solvents for minimizing isomerization. Aminolysis at the wrong carbonyl of the anhydride of a peptide (path F) is less than that for the anhydride from the corresponding /V-alkoxycarbonylamino acid. 

NL Benoiton, Y Lee, FMF Chen. Isopropyl chloroformate as a superior reagent for mixed anhydride generation and couplings in peptide synthesis. Int J Pept Prot Res 31, 577, 1988. 

Use the mixed-anhydride method in dimethylformamide with isopropyl chloroformate as me reagent and (V-methylmorpholine, A -melhylpiperi-dine, or trimethylpyridine as me base (see Sections 7.4 and 7.5). 

In 2000, Reddy and colleagues developed a one-step conversion of carboxylic acid to hydroxamic acid under neutral pH conditions using ethyl chloroformate as an activating reagent (Scheme 50). 

Sodium methoxide in methanol, often with chloroform as cosolvent, has customarily been the basic reagent employed. Less frequently, particularly with water-soluble esters, sodium or potassium hydroxide in aqueous solution has been used. Generally, an excess of the basic reagent is taken, except where the possibility of epoxide migration arises (see p. 127). In the latter situation, only a limited excess of reagent is used, at low temperature, or, alternatively, the... 

The reaction of a similar charge of reagents, but using chloroform as the solvent. 

The synthesis of the peptide-based triazole 63 is shown in Scheme 19J102l Coupling of Boc-Ser(Bzl)-OH (61) with ethyl ox am i drazon ate11131141 proceeded under mixed anhydride conditions177 using ethyl chloroformate as the activating reagent. The product acylamidrazone 62 thus formed was simply heated in xylenes under Dean-Stark conditions to form the desired triazole 63. 

Chloromethylation.1 Chloromethyl methyl ether has been generally used for electrophilic aromatic chloromethylation, but it is highly toxic and now considered a carcinogen. Chloromethylation can be effected by use of a trimethylsilyl ether (1) of a chlorohydrin prepared as shown from trioxane and chlorotrimethylsilane in the presence of stannic chloride in chloroform. This reagent, generated in situ, is effective for chloromethylation of styrene in the presence of SnCl4 any excess is easily decomposed by hydrolysis. Bromomethylation is possible by replacement of ClSi(CH3)3 by BrSi(CH3)3. 

There are several types of chiral derivatizing reagents commonly used depending on the functional group involved. For amines, the formation of an amide from reaction with an acyl halide [147,148], chloroformate reaction to form a carbamate [149], and reaction with isocyanate to form the corresponding urea are common reactions [150]. Carboxyl groups can be effectively esterified with chiral alcohols [151-153]. Isocynates have been used as reagents for enantiomer separation of amino acids, iV-methylamino acids, and 3-hydroxy acids [154]. In addition to the above-mentioned reactions, many others have been used in the formation of derivatives for use on a variety of packed and capillary columns. For a more comprehensive list, refer to References 155-159. 

Lead(IV) acetate is most commonly employed to plumbylate arenes, often using chloroform as the solvent. Being a relatively weak electrophile, Pb(OAc)4 can react only with electron-rich aromatic compounds, for example anisole and polyalkoxy-benzenes. The electrophilicty of the lead reagent is, however, enhanced substan-... 

Tellurium (O-ethyl dithiocarbonate) chloride was similarly obtained using tellurium tetrachloride as reagent and dichloromethane as the solvent. The reaction was carried out at 20°. After stirring of the reaction mixture for 2 h, the solvent was evaporated under reduced pressure. The residue was washed with boiling light petroleum ether and then recrystallized from chloroform/light petroleum ether2. 

Arsenic was analysed chromatographically by Schwedt and Russel [617], It was first extracted from biological material into chloroform as the dithiocarbamate, which was converted into triphenylarsine(III) by the treatment with phenyl-Grignard reagent. In this form it was subjected to GC analysis with the use of an FID. Concentrations of arsenic down to 2 jug per gram of biological sample was measured. 

Reagents and Solutions Use the Periodic Acid Solution, Potassium Iodide Solution, and Chloroform as described under 1-Monoglycerides, in this Appendix. 

The most widely used and, presumably, the most chemoselective reagents for the epoxidation of nucleophilic C—C double bonds are the peroxycarboxylic acids (see Houben-Weyl, Vol. IV/ 1 a, p 184, Vol. Vl/3, p 385, Vol. E13/2, p 1258). Using chloroform as solvent, epoxidation rates are particularly high79. Reactive or acid/base sensitive epoxides can often be obtained with dimethyldioxirane (see Houben-Weyl, Vol. R13/2, p 1256 and references 15, 16, 87-90), peracid imides (see Houben-Weyl, Vol. IV/1 a, p 205, Vol. VI/3, p 401, Vol. E13/2, p 1276) (prepared in situ from nitriles and hydrogen peroxide), hydroperoxy acetals (see Houben-Weyl, Vol. El3/2, p 1253) or peroxycarbonic acid derivatives (see Houben-Weyl, Vol. IV/la, p 209 and references 17-19) as oxidants. For less reactive alkenes, potassium hydrogen persulfate is a readily available reagent for direct epoxidation20. 

Olofson and coworkers also introduced vinyl chloroformate as a reagent for the N-dealkylation of tertiary amines (Ref. 157,158,159). Compared with commonly utilized reagents in N-dealkylation procedures, the use of VOC-CI leads to significantly improved yields under milder conditions combined with greater discrimination between alkyl groups in unsymmetrical amines. The procedure is illustrated by the selective N-deethylation of N-ethyl piperidine to afford piperidine.HCI in 90% yield (Ref. 159) as depicted in scheme 107. 

Oxides and peroxides can occur in many essential oils by a photochemical reaction. 1,8-Cineol and linalool monoxide can be readily separated on silica gel thin layers with 1-nitropropane-hexane (1 1, v/v), as the mobile phase.In this case, they have exhibited Rf values of 73 and 8, respectively. " Another pair of compounds, ascaridole and 1,8-cineol, can be easily separated on a silica gel layer, obtaining a value for chloroform as the mobile phase of 63 and 54, respectively. The antimony chloride reagent gives a gray color. The potassium iodide-acetic acid-starch test is usually better than ferrous thiocyanate. 

I he imhydrotis reagent in methylene chloride or chloroform as solvent served bifll for the oxidalion of anilines to nitrobenzenes, particularly those with negative tUhiitilncnlN. In the example cited the solvent was chloroform, and the yield is... 

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