Hydroxyls with Chloroacetic Acid

The following protocol illustrates the modification of a dextran polymer with chloroace-tic acid. 

In a fume hood, prepare a solution consisting of 1M chloroacetic acid in 3 M NaOH. 

Immediately add dextran polymer to a final concentration of 40mg/ml. Mix well to dissolve. 

React for 70 minutes at room temperature with stirring. 

Stop the reaction by adding 4mg/ml of solid NaH2P04 and adjusting the pH to neutral with 6N HC1. 

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A method for replacing thiol by hydroxyl groups consists of treating them with chloroacetic acid, which converts them into sulfide groups these products are hydrolysed to the hydroxy compound and mercaptoacetic acid, partly already in hot water but completely only under the action of hot concentrated hydrochloric acid ... 

Figure 11.9 is a quantitative C-NMR spectrum of the carbonyl region of the end-capped ethoxylate discussed in sections 11.6.1 and 11.6.2. This carboxylic acid can be made either by reacting the alcohol ethoxylate with chloroacetic acid or by catalytic oxidation of the terminal hydroxyl of the ethoxylate itself. In either event, the product can react with remaining alcohol to form an ester, an undesirable by-product. 

A, 0-carboxymethyl chitosan (N,0-CC) is a chitosan derivative that has carboxymethyl substituents at some of both the amine and the 6-hydroxyl sites of its glucosamine units. It can be easily prepared using chitosan, sodium hydroxide, and isopropanol with chloroacetic acid [65]. N,0-CC as a wound dressing can stimulate the extracellular lysozyme activity of fibroblasts and considerably promote the proliferation of skin fibroblasts. N,0-CC is also used in the development of various functional hydrogels, including superporous or pH-sensitive hydrogels, which are used for protein drug delivery [66-69]. 

Another approach uses reactive alkyl halogen compounds containing a terminal carboxylate group on the other end to form spacer arms off the dextran polymer from each available hydroxyl. In this manner, Brunswick et al. (1988) used chloroacetic acid to modify the hydroxyl groups to form the carboxymethyl derivative. The carboxylates then were aminated with ethylene diamine to create an amine-terminal derivative (Inman, 1985). Finally, the amines were modified with iodoacetate to form a sulfhydryl-reactive polymer (Figure 25.14). 

Figure 25.14 An amine derivative of dextran may be prepared through a two-step process involving the reac-tion of chloroacetic acid with the hydroxyl groups of the polymer to create carboxylates. Next, ethylene diamine is coupled in excess using a carbodiimide-mediated reaction to give the primary amine functional groups.

In other studies [34,186], the treatment of trichloroethylene and tetrachloroethylene with UV/H202 system is reported. For example, Beltran et al. [34] determined the rate constants of the reactions between hydroxyl radical and TCE and TCA with this oxidizing system at high concentration of hydrogen peroxide. Hirvonen et al. [186] observed the formation of chloroacetic acids during the hydrogen peroxide photo-assisted oxidation of tri- and tetrachloroethylene. These authors [186] report that formation of chloroacetic acids diminishes when hydrogen peroxide is simultaneously applied to UV radiation compared to UV radiation alone. 

The relative strengths of weakly basic solvents are evaluated from the extent of protonation of hexamethylbenzene by trifluoro-methanesulfonic acid (TFMSA) in those solvents or from the effect of added base on the same protonation in solution in trifluoroacetic acid (TFA), the weakest base investigated. The basicity TFA < di-fluoroacetic acid < dichloroacetic acid (DCA) < chloroacetic acid < acetic acid parallels the nucleophilicity. 2-Nitropropane appears to be a significantly stronger base than DC A by the first approach, although in the second type of measurement, the two have essentially equal basicity. The discrepancy is due to an interaction, possible for hydroxylic solvents such as DC A, with the anion of TFMSA. This anion stabilization is a determining factor of carbocationic reactivity in chemical reactions, including solvolysis. A distinction is made between carbocation stability, determined by structure, and persistence (existence at equilibrium, e.g., in superacids), determined by environment, that is, by anion stabilization. 

In the previous chapters the preparation and properties of certain important classes of compounds have been discussed, and the principles which are illustrated in their transformations into one another have been emphasized. These principles are of wide application and can be employed in the preparation of compounds of more complex structure than any met with so far. For example, the method of preparing an alcohol by the treatment of an alkyl halide with water or an alkali, is very general in its application. The reaction consists in the replacement of a halogen atom by a hydroxyl group, and such replacement takes place not only with alkyl halides, but with other compounds which contain halogen. Thus, chloroacetic acid can be transformed into hydroxyacetic acid by water —... 

Halogen-substituted acids are also prepared by the action of the halides of phosphorus on hydroxy-acids hydroxyacetic acid, CH2OH.COOH, for example, is converted into chloroacetyl chloride by phosphorus pentachloride, both hydroxyl groups taking part in the reaction. The substituted acetyl chloride reacts readily with water and chloroacetic acid and hydrochloric acid are formed —... 

Condensation of salicylaldehyde and its derivatives with a variety of esters of chloroacetic acids in the presence of TBAB led to the synthesis of benzo[b]furans by means of a solid-liquid PTC reaction under the action of microwave irradiation [39]. This was a modification of one of the most popular routes to substituted benzo[b]furans, i.e. O-alkylation of O-hydroxylated aromatic carbonyl compounds with a-halogenated carbonyl compounds then intramolecular condensation. The mixture of aldehydes and chloroacetic acid esters were absorbed on potassium carbonate then irradiated in an open vessel in a domestic MW oven for 8-10 min (Eq. 26). 

Chemical/Physical. Hydrolyzes in distilled water at 25°C forming 2-chloro-3-propenol and hydrochloric acid. The lialf-life was 1 day (Milano et al., 1988 Kolhg, 1993). Chloroacetaldehyde, formyl chloride and chloroacetic acid were formed from the ozonation of dichloropropylene at about 23°C and 730 mmHg. Chloroacetaldehyde and formyl chloride also formed from the reaction of dichloropropylene with hydroxyl radicals (Tua-zon et al., 1984). 

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