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Working trichloroacetic acid

The transformation of carboxylic acids with CDI into imidazolides has a wide range of applicability. CDI reacts with aliphatic, aromatic, and heterocyclic carboxylic acids under very mild conditions, and these reactions are not affected by the presence of functional groups unless the latter are strongly nucleophilic and themselves react with CDI in such cases a reversible protection of the functional groups is necessary. The reaction of CDI also works in such specific cases as trifluoro- and trichloroacetic acids, leading to the very reactive Af-trifluoro- and N-trichloroacetylimidazoles. 1 111... [Pg.28]

In this paper the author presents some of his contributions to the theory and practice of the cationic polymerisation (CP) of alkenes since 1944. The first phase of his work at the University of Manchester comprises the discovery of co-catalysis by water with TiCl4, the invention of the pseudo-Dewar reaction vessel, the use of trichloroacetic acid as co-catalyst, and the disproof of the alleged cationic isomerisation of cis-stilbene. [Pg.18]

The walls of Gram-positive bacteria, unlike the membranes, sometimes do not contain teichoic acids. However, there are numerous examples of walls which do contain these compounds in substantial proportions, although in relatively few cases has detailed structural work been carried out. The purification of wall teichoic acids is often much more readily achieved than for the membrane polymers. Addition of ethanol to trichloroacetic acid extracts of walls gives a precipitate which is usually pure teichoic acid. Extraction is effected at low temperatures, and for a reasonably short time, in order to avoid extensive degradation of the polymers under the acidic conditions. Consequently, although walls may contain 20-50% by weight of teichoic acid, practiced yields are generally rather low. [Pg.346]

The nature of the association between membrane and teichoic acid is unknown, and it is possible that these teichoic acids are chemically attached to other components of the cell. Samples obtained by extraction with phenol appear to have appreciably higher molecular weight than has the purified teichoic acid obtained by extraction with trichloroacetic acid, and it is likely that the prolonged, acid treatment used in earlier work may have caused hydrolysis of some of the phosphodiester linkages. It is noteworthy that this comment on earlier studies does not apply to ribitol teichoic acids. Detailed examination of preparations of membrane teichoic acid obtained by less drastic conditions is highly desirable, in order to confirm the supposed size of the naturally occurring polymers, as well as... [Pg.367]

Precipitate the protein with trichloroacetic acid (TCA) and deoxycholate (DOC), dissolve pellet in BCA working reagent Treat the sample with iodoacetamide (for thiols)... [Pg.84]

In any quantitative work on protein hydrolysis, it is necessary to have a measure of the extent of the hydrolytic degradation. The measurement of the number of peptide bonds cleaved during a hydrolytic process is related to the activity of proteinolytic enzymes and the extent of hydrolysis. Various techniques that evaluate the progress of hydrolysis have been reported, such as the trichloroacetic acid (TCA) solubility index, which evaluates the percentage of nitrogen soluble in TCA after partial hydrolysis of the protein. [Pg.152]

Future work. With modifiers less polar than methanol, low concentrations of some additives dramatically increase the apparent solvent strength of ternary mixtures, as shown in Figure 8. Thus, 20 % methylene chloride containing 1.0 % trichloroacetic acid (TCA) produces an apparent solvent strength greater than pure methanol (compare Figures 4 8). [Pg.145]

All three chloroacetic acids (chloroacetic acid [MCA], dichloroacetic acid [DCA], and trichloroacetic acid [TCA]) are naturally occurring (7), with TCA being identified in the environment most frequently (reviews (278, 405 108)). However, these chlorinated acetic acids also have anthropogenic sources. The major source of natural TCA appears to be the enzymatic (chloroperoxidase) or abiotic degradation of humic and fulvic acids, which ultimately leads to chloroform and TCA. Early studies (409) and subsequent work confirm both a biogenic and an abiotic pathway. Model experiments with soil humic and fulvic acids, chloroperoxidase, chloride, and hydrogen peroxide show the formation of TCA, chloroform, and other chlorinated compounds (317, 410-412). Other studies reveal an abiotic source of TCA (412, 413). [Pg.26]

The earlier work on the isolation of PolyPs from the cells of living organisms usually employed the same methods as those used for the extraction of nucleic acids. It was not until 1936 that MacFarlane (MacFarlane, 1936) proposed a specific method for the extraction and fractionation of condensed phosphates present in cells. It was found that these phosphates could be divided into two main fractions, i.e. one soluble in 5 % trichloroacetic acid (TCA) and the other insoluble, and ever since then cellular condensed polyphosphates have been divided into acid-soluble and acid-insoluble fractions. [Pg.15]

On the basis of theoretical studies by Bach and co-workers,17 it was found that the nucleophilic 71-bond of the alkene attacks the 0-0 cr-bond in an Sn2 fashion with displacement of a neutral carboxylic acid. There are, however, some mechanistic anomalies. For example, a protonated peracid should be a much more effective oxygen transfer agent over its neutral counterpart, but experiments have shown only modest rate enhancements for acid catalysed epoxidation. Early attempts to effect acid catalysis in alkene epoxidation where relatively weak acids such as benzoic acid were employed proved unsuccessful.18 The picture is further complicated by contradictory data concerning the influence of addition of acids on epoxidation rates.19 Trichloroacetic acid catalyses the rate of epoxidation of stilbene with perbenzoic acid, but retards the rate of a double bond containing an ester constituent such as ethyl crotonate.20 Recent work has shown that a seven-fold increase in the rate of epoxidation of Z-cyclooctene with m-chloroperbenzoic acid is observed upon addition of the catalyst trifluoroacetic acid.21 Kinetic and theoretical studies suggest that the rate increase is due to complexation of the peroxy acid with the undissociated acid catalyst (HA) rather than protonation of the peroxy acid. Ab initio calculations have shown that the free energy of ethylene with peroxy-formic acid is lowered by about 3 kcal mol-1 upon complexation with the catalyst.21... [Pg.82]

The standard curve is set up from malonyldialdehyde prepared from freshly hydrolysed malonyldialdehydebisacetal the standard (1 g/ml) is diluted 1 1000 in phosphate-buffered saline and diluted again 1 1000 to a working concentration of 1 ng//d. Tubes containing a range of aliquots from the diluted stock, ranging from 100 fA up to 500 fA, were brought up to a volume of 0.8 ml and then the thiobarbituric acid and the trichloroacetic acid added as described above for the samples. [Pg.80]

The mechanism of dimerisation of these compounds has been the subject of many recent studies, but the pioneering work of Evans and collaborators with trichloroacetic acid as catalyst is to be considered as the starting point of a long series of interesting investigations. These authors took a number of diaiyl ethylenes and studied the kinetics of their dimerisation and of the reverse reaction, the thermodynamics of the equilibria involved and the electronic spectra of the intermediate species. Benzene was normally used as solvent, but nitroethane was also tried with 1,1-diphenylethylene. [Pg.57]

The catalytic activity of hydrogen chloride was found by Tarbell and Kincaid 34g). Continuing this work, Tarbell et al. 36) showed that certain acids and bases affect the yields of urethanes obtained from a-naphthyl isocyanate and phenols. Thus, catalytic effects were observed with sodium carbonate and acetate, pyridine, triethylamine, acetic acid, trichloroacetic acid, zinc chloride, hydrogen chloride, and boron fluoride etherate. The latter catalyst and triethylamine were found to be the most effective acidic and basic catalysts, respectively. [Pg.409]

It is also possible to self-condense 1,9-diunsubstituted dipyrromethanes in the presence of a one-carbon unit (formaldehyde, orthoformic ester). Because of the non-nucleophilicity of protonated dipyrromethenes (e.g., (41)) this approach only works well for dipyrromethanes. Using this methodology, and with trimethyl orthoformate as the one-carbon unit and trichloroacetic acid as the catalyst, coproporphyrin-II tetramethyl ester (71) can be obtained in good yield from the dipyrromethane-1,9-dicarboxylic acid (72) (Scheme 21) 45... [Pg.504]

Data from Imbriani et al. (1988) are presented in Figure 2-4. Monster (1986) proposed that the best method for estimating occupational exposure to 1,1,1-trichloroethane was to determine the levels of 1,1,1-trichloroethane and trichloroacetic acid in blood after work on Fridays. [Pg.102]

Carbon tetrachloride (5.6 g, 36.5 mmol) is dissolved in THF (100 mL) and cooled to -105 °C. Butyllithium in hexane (26 mL, 37 mmol), is then added over a 30 min period. There occurs a mild exotherm and a very gradual change from colorless to pale pink. After about half the butyllithium is added, a white precipitate becomes visible. After 1 h from the start, the reaction is a white slurry (very clean looking). After 1.5 h, the reaction is poured onto stirred powdered Dry Ice and worked up as before. All of the acid distilled at 69.5 °C (0.4 mm) and crystallized in the condenser. 4.5 g of trichloroacetic acid is isolated (76% yield). The infrared spectum is identical with that of an authentic sample. [Pg.326]


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See also in sourсe #XX -- [ Pg.196 ]




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Trichloroacetic acid

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