Unreacted acid

The reaction commences at about 120° the carbamic acid formed decomposes immediately into carbon dioxide and ammonia. The latter may form the ammonium salt with unreacted acid the ammonium salt also reacts with urea at temperatures above 120° to yield the amide ... 

The esterification reaction in making ester oils is commonly carried out with a catalyst at about 210°C while removing excess water as it forms (32). Excess acid or alcohol is then stripped off, and unreacted acid is neutrali2ed with calcium carbonate or calcium hydroxide before final vacuum drying (qv) and filtration (qv). 

Perchloric acid can be prepared by the treatment of perchlorates with sulfuric acid followed by distillation. A modification of the procedure (21) involves the reaction of ammonium perchlorate with nitric and hydrochloric acids, and then concentration at 198—200°C to eliminate the unreacted acids by vacuum distillation ... 

The water formed in the reaction is continuously removed from the reaction mixture by azeotropic distillation, in order to avoid reversible reaction between water and ester. The progress of reaction can be followed either by measuring the amount of water or by determining the amount of unreacted acid in aliquots withdrawn at regular intervals of time. The reaction can be carried out either in presence of a catalyst, i.e. a weak acid like p-toluene sulphonic acid (a strong acid can hydrolyse the polymer, formed) or in absence of the catalyst. 

Hydrolysis of unreacted acid chloride is carried out without neutralization of the acid generated. In the presence of a base such as sodium carbonate or sodium bicarbonate the anhydride of 2-toluic acid would be formed, in addition to the sodium salt of the free acid. This anhydride is much less reactive toward hydrolysis than the acid chloride. 

The unreacted acid is neutralized by lime, treated with water, and the solution filtered to separate any excess Mn02 and insoluble residues. Evaporation of the filtrate yields a crude product containing about 80% MnS04 and 15% (NH4)2S04. 

After a 2.0-min reaction time (two bonds broken per molecule urea), addition of excess HC1 stops the reaction and converts the carbamate to ammonium ion. Back titration with NaOH estimates the unreacted acid. 

While still useful for large-scale esterification of fairly robust carboxylic acids, Fischer esterification is generally not useful in small-scale reactions because the esterification depends on an acid-catalyzed equilibrium to produce the ester. The equilibrium is usually shifted to the side of the products by adding an excess of one of the reactants—usually the alcohol—and refluxing until equilibrium is established, typically several hours. The reaction is then quenched with base to freeze the equilibrium and the ester product is separated from the excess alcohol and any unreacted acid. This separation is easily accomplished on a large scale where distillation is often used to separate the product from the by-products. For small-scale reactions where distillation is not a viable option, the separation is often difficult or tedious. Consequently Fischer esterification is not widely used for ester formation in small-scale laboratory situations. In contrast, intramolecular Fischer esterification is very effective on a small scale for the closure of hydroxy acids to lactones. Here the equilibrium is driven by tire removal of water and no other reagents are needed. Moreover the closure is favored entropically and proceeds easily. 

Arylpropionic acids are important class of non-steroidal anti-inflammatory drugs (NSAID). Their pharmacological activity is mainly in one of both enantiomers. Thus, efforts had been made to access to the enantiomerically pure substance. The kinetic resolution of racemic 2-(2-fluoro-4-biphenyl) propanoic acid 56 and 2(4-isobutylphenyl) propanoic acid 59 (Ibuprofen) was performed via enzymatic esterification and transesterification using an alcohol and vinyl acetate, respectively in a membrane reactor. The unreacted acid is obtained in highly enantiomerically enriched form. A consecutive approach consisting of the enzymatic hydrolysis of the resulted esters is needed to achieve the alcohol in optically pure form.77... 

In an alternative approach to prepare the chiral side chain of captopril (14) and zofenopril (18), the lipase-catalyzed stereoselective esterification of racemic 3-benzoylthio-2-methylpropionic acid (19) (Fig. 8B) in an organic solvent system was demonstrated to yield i -(+)-methyl ester (20) and unreacted acid enriched in the desired S-( )-enantiomer (19) [45], Using lipase PS-30 with toluene as solvent and methanol as nucleophile, the desired S-(-)-(19) was obtained in 37% reaction yield (theoretical max. 50%) and 97% e.e. Substrate was used at 22-g/ liter concentration. The amount of water and the concentration of methanol supplied in the reaction mixture was very critical. Water was used at 0.1 % concentration in the reaction mixture. More than 1% water led to the aggregation of enzyme in the organic solvent, with a decrease in the rate of reaction which was due to... 

There is still a lack of acidic poisons and the search for suitable and unreactive acidic compounds is strongly needed. Furthermore, the study of the chemisorp-tive behavior of bifunctional molecules, such as diketones, diamines, and cyclic compounds such as diazines (400), with two heteroatoms in varying relative orientations seems to be promising, since such compounds may shed some light on the configurations of exposed cations and on their geometric arrangements in the exposed crystal faces. 

The first five compounds (two acid chlorides and three anhydrides1) are all reactive acid derivatives, and the five esters and amides below them are all unreactive acid derivatives and yet the C=0 shifts of all ten compounds fall in the same range. The C=0 chemical shift is obviously not a good way to check on chemical reactivity. 

The mixture of unreacted acid, water, and anhydride is fed to a still, which yields dilute acetic acid overhead and an anhydride-acetic acid mixture at the bottom (see Fig. 12.11). Conditions are controlled in such a way that the raffinate is about 40 percent anhydride and 60 percent acetic acid. As already mentioned, this is the desired ratio for the reaction mixture used for acetylation of cellulose. 

Benzodiazocine 264 was prepared through a 4-component Ugi reaction including a primary amine tethered to a BOC-protected internal amino nucleophile, followed by a postcondensation base-catalyzed cyclization. Thus, 2 equiv of aldehyde 262 were employed to promote Schiff base formation and a one-pot, double scavenging protocol with immobilized tosylhydrazine and di-isopropylethylamine removed both the excess aldehyde and any unreacted acid 261. The intermediate 263 was then subjected to treatment with TFA, followed by proton scavenging with resin bound morpholine, to promote cyclization to afford the eight-membered ring (Scheme 47) <2001TL4963>. 

Sulfides are strong nucleophiles but weak bases and, therefore, they deactivate carbocations more strongly than protonic acids. This reduces the relative rate of propagation and increases the ratio of the rate of initiation to that of propagation. For example, when equimolar amounts of isobutyl vinyl ether and triflic acid are mixed, even at -78° C, a polymer and the unreacted acid are observed. Under similar conditions in the presence of an excess sulfide (R2S), a monomeric sulfonium salt is the only product ... 

You are working for a company that many years ago conducted a number of polycondensation reaction experiments between diol and diacid monomers. You need data on the kinetics of one of these reactions from the archives, but much was lost in a flood. All you find are the results of the original experiments, where small aliquots of sample were withdrawn from the reaction vessel, quenched to low temperature to stop the reaction and titrated to determine the amount of unreacted acid functional groups. The results... 

The diazoalkanes are not isolated but are collected in ether for immediate consumption. The quantity and yield from the N-nitroso compound are determined by tteating an aliquot with excess benzoic acid and titrating the unreacted acid with standard alkali, The diazoalkanes should be handled with care. ... 

In conventional reactive distillation the desired conversion can not be reached. However, because the unreacted acid will not end up in the bottom stream, it is possible to have a product purity of 99.9% which is not the case in the other configurations. 

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