Chloroformate functions, conversion

Figure 2. Conversion of chloroformate functions corresponding to different triads (i,h,s) vs the degree of substitution of the polymer.

Analyses of the chloroform-soluble extracts of the subbituminous coal by Fourier transform infrared spectroscopy (FTIR) showed the presence of a sharp carbonyl absorption peak (1800-1650 cm ) in the extracts from the parent coal and in those obtained at yields less than about 10% wt dmmf. The peak, which is attributed to ketones and carboxylates, disappeared at higher conversions (16). Whitehurst and co-workers (12) established that carbonyl- containing compounds, such as esters and carboxylates, can cleave under thermal treatment to produce CO, CO2 and phenols. They concluded that the evolution of these gases during coal liquefaction could originate from the decomposition of similar oxygen functionalities in the coal. 

Sodium cholate is insoluble in chloroform and in nonpolar solvents in general, but it is very soluble in alcohol and in water. Lecithin, on the contrary, is soluble in chloroform and only swells in water without dissolving in it. These differences in solubility are evidently related to the molecular structure and to the position of the hydrophilic groups in each of these molecules. The lecithin molecule has two important paraffinic chains and a group of hydrophilic functions (choline phosphate) localized at one end. In the presence of water, the lecithin molecules are oriented with their hydrophilic groups toward the water, and they hide their paraffinic chains inside a structure formed of two superposed layers of molecules. Conversely, in a nonpolar solvent the paraffinic chains are turned toward the solvent, while the polar groups are hidden inside the micelle. 

Solutions of triethylamine (Et3N) 14 (1.0M), premixed carboxylic acid/alkyl chloroformate (1.0 M respectively), and 4-dimethylaminopyri-dine 15 (0.5 M) in MeCN were introduced into the reactor from separate inlets and the reaction products collected at the outlet in MeCN, prior to analysis by gas chromatography-mass spectrometry (GC-MS). Under optimized reaction conditions, the authors were able to synthesize the methyl 16, ethyl 17, and benzyl 18 esters in quantitative conversion, with no anhydride or deprotection by-products detected (as observed in conventional batch reactions). In addition to the Boc-glycine derivatives illustrated in Scheme 4, the authors also esterified a series of aromatic carboxylic acids with yields ranging from 91 to 100%, depending on the additional functional groups present. 

For a carboxylic acid and an amine to form an amide, the carboxylic acid usually must be activated that is, it must be converted to a more reactive functional group. Conversion to an acyl chloride is a common way to accomplish this for normal organic reactions (see Chapter 19). However, acyl chlorides are quite reactive and do not give high enough yields in peptide synthesis because of side reactions. Therefore, milder procedures for forming the amide bond are usually employed. In one method the carboxylic acid is reacted with ethyl chloroformate (a half acyl chloride, half ester of carbonic acid) to produce an anhydride. Treatment of this anhydride with an amine results in the formation of an amide ... 

In amino acid and peptide chemistry, the di-ferf-butyl dicarbonate (BocaO) is an extensively used reagent for the clean and rapid Boc-protection of amine functionalities.It is also an efficient ferf-butoxycarbonylating agent for alcohols, thiols, and carbon nucleophiles, and it has been used for the conversion of amines into isocyanates, carbamates, and urea derivatives.The reaction of amino acids with chloroformates to produce N-urethane-protected amino acids if not performed under optimal conditions is accompanied by the formation of N-protected oligomers this has been well documented in the case of and... 

The same authors also published a simple one-pot protocol for the azide to carbamate transformation using a variety of chloroformates.21 This preparation is excellent for azide to carbamate transformations (such as Cbz, Troc, and Alloc) that would clearly not be feasible via the one-pot catalytic hydrogenation/protection preparations due to functional group incompatibility. Trimethylphosphine is the phosphine of choice once again. As the rapid and room temperature conversion of 33 to intermediate 34 illustrates, the use of trimethylphosphine allows for excellent yields under mild conditions. 

In contrast to the reaction of pristinamycin 11 with acid anhydrides, where acylation was only observed with acetic anhydride, the reaction of pristinamycin IIa with acid chlorides (Scheme 10) was demonstrated to be of greater synthetic utility. However, the course of acylation depended strongly on the reactivity of the acid chloride. For example, the reaction of pristinamycin 11 with ethyl malonyl chloride in the presence of triethylamine or pyridine resulted in a quantitative conversion by tic into the ester (50, R = CH2C02Et, 60% isolated yield) whereas the use of more reactive acyl chlorides, for example ethyl chloroformate resulted in acylation of the 37-ketone function as its enol ether (see Sect. 5.4.2). If the acylation reagents were used in excess, a diacylated derivative pf the enol form of pristinamycin 11 (51) was obtained. 

Post-polymerization functionalization has also been applied to the synthesis of terpyridine-modified polymers [ 126]. In a recent approach, Schubert and colleagues employed this method to prepare poly(pentafluorostyrene) with terpyridines in the side chains [127]. First, poly(pentafluorostyrene) with a narrow polydispersity index of just 1.08 was synthesized by nitroxide-mediated polymerization. In a second step, this polymer was converted with amine-functionalized terpyridine under microwave heating, selectively substituting the para-fluorines. Addition of iron(II) sulfate to a solution of the terpyridine-functionalized polymer in a mixture of chloroform and methanol leads to gelation at a polymer concentration of 33 g In another work, Schubert and coworkers prepared metal-cross-Iinked polymer networks from linear and tri-arm PEG precursors, both functionalized with terpyridine at their OH-termini [128]. Quantitative functionalization of these precursors was achieved by conversion of the hydroxy-functionalized PEG derivatives with 4-chloro-2,2 6, 2"-terpyridine under basic conditions. However, quantitative cross-linking with iron(II) chloride was not observed in methanol solutions, neither at room temperature nor at elevated temperature, but only a small quantity of cross-linked material precipitated from the solution. This observation was attributed to a strong tendency of the tri-arm PEG to form intramolecular complexes, acting as a chain stopper rather than as a cross-linker. 

---