Side reactions acids

It was observed that the presence of sulphuric acid promotes the hydrolysis of esters (e.g. [104,107,109]). The rate of hydrolysis is for the most part significantly lower than the esterification rate. Moreover, as already discussed above, in addition to the main reaction producing alcohol and nitrating acid, the hydrolysis process is generally accompanied by side reactions. Acids other than sulphuric, or perchloric [104], e.g. acetic [106] or phosphoric, if present in the esterifying mixture, hydrolyse esters to a markedly smaller extent than sulphuric acid. The acid make up of an esterification mixture in industry is established experimentally. Economic factors also plays a part here. 

Cysteine-containing peptides are particularly prone to base-mediated side reaction. Acid-labile linker-bound C-terminal Cys undergoes significant racemization (approximately 0.5%) with each cycle of piperidine treatment [73]. This could be reduced to a modest level (0.1%) by use of 1% DBU in DMF [59]. However, both piperidine and DBU were observed to cause dehydration of C-terminal cysteine residues to a 3-(l-piperidinyl)alanine or dehydroalanine [74]. No measures could be found to prevent completely this partially side chain protection- and sequence-dependent problem. Recourse to Boc-SPS may be necessary. 

The gas is passed through caustic soda solution to remove any sulphur dioxide or carbon dioxide produced in side reactions. Carbon monoxide is also obtained when an ethanedioate (oxalate) is heated with concentrated sulphuric acid ... 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

More information has appeared concerning the nature of the side reactions, such as acetoxylation, which occur when certain methylated aromatic hydrocarbons are treated with mixtures prepared from nitric acid and acetic anhydride. Blackstock, Fischer, Richards, Vaughan and Wright have provided excellent evidence in support of a suggested ( 5.3.5) addition-elimination route towards 3,4-dimethylphenyl acetate in the reaction of o-xylene. Two intermediates were isolated, both of which gave rise to 3,4-dimethylphenyl acetate in aqueous acidic media and when subjected to vapour phase chromatography. One was positively identified, by ultraviolet, infra-red, n.m.r., and mass spectrometric studies, as the compound (l). The other was less stable and less well identified, but could be (ll). 

I ve found that unfortunately, there is a hyper oxydation of oleofin as side reaction, and gives organic acids, probably MDPhenylace-tic acid and may be a bit of piperonylic acid. It s easy to realise it. 

This is a way to do this procedure without having to use one of those crazy tube furnaces stuffed with thorium oxide or manganous oxide catalyst [21]. The key here is to use an excess of acetic anhydride. Using even more than the amount specified will insure that the reaction proceeds in the right direction and the bad side reaction formation of dibenzylketone will be minimalized (don t ask). 18g piperonylic acid or 13.6g phenylacetic acid, 50mL acetic anhydride and 50mU pyridine are refluxed for 6 hours and the solvent removed by vacuum distillation. The remaining residue is taken up in benzene or ether, washed with 10% NaOH solution (discard the water layer), and vacuum distilled to get 8g P2P (56%). 

Diethyl 3-oxoheptanedioate, for example, is clearly derived from giutaryl and acetic acid synthons (e.g. acetoacetic ester M. Guha, 1973 disconnection 1). Disconnection 2 leads to acrylic and acetoacetic esters as reagents. The dianion of acetoacetic ester could, in prin-ciple,be used as described for acetylacetone (p. 9f.), but the reaction with acrylic ester would inevitably yield by-products from aldol-type side-reactions. 

Then N-Boc-O-benzylserine is coupled to the free amino group with DCC. This concludes one cycle (N° -deprotection, neutralization, coupling) in solid-phase synthesis. All three steps can be driven to very high total yields (< 99.5%) since excesses of Boc-amino acids and DCC (about fourfold) in CHjClj can be used and since side-reactions which lead to soluble products do not lower the yield of condensation product. One side-reaction in DCC-promoted condensations leads to N-acylated ureas. These products will remain in solution and not reaa with the polymer-bound amine. At the end of the reaction time, the polymer is filtered off and washed. The times consumed for 99% completion of condensation vary from 5 min for small amino acids to several hours for a bulky amino acid, e.g. Boc-Ile, with other bulky amino acids on a resin. A new cycle can begin without any workup problems (R.B. Merrifield, 1969 B.W. Erickson, 1976 M. Bodanszky, 1976). 

The synthesis described met some difficulties. D-Valyl-L-prolyl resin was found to undergo intramolecular aminoiysis during the coupling step with DCC. 70< o of the dipeptide was cleaved from the polymer, and the diketopiperazine of D-valyl-L-proline was excreted into solution. The reaction was catalyzed by small amounts of acetic acid and inhibited by a higher concentration (protonation of amine). This side-reaction can be suppressed by adding the DCC prior to the carboxyl component. In this way, the carboxyl component is "consumed immediately to form the DCC adduct and cannot catalyze the cyclization. 

Until now we have been discussing the kinetics of catalyzed reactions. Losses due to volatility and side reactions also raise questions as to the validity of assuming a constant concentration of catalyst. Of course, one way of avoiding this issue is to omit an outside catalyst reactions involving carboxylic acids can be catalyzed by these compounds themselves. Experiments conducted under these conditions are informative in their own right and not merely as means of eliminating errors in the catalyzed case. As noted in connection with the discussion of reaction (5.G), the intermediate is stabilized by coordination with a proton from the catalyst. In the case of autoprotolysis by the carboxylic acid reactant, the rate-determining step is probably the slow reaction of intermediate [1] ... 

Many of the reactions listed at the beginning of this section are acid catalyzed, although a number of basic catalysts are also employed. Esterifications are equilibrium reactions, and the reactions are often carried out at elevated temperatures for favorable rate and equilibrium constants and to shift the equilibrium in favor of the polymer by volatilization of the by-product molecules. An undesired feature of higher polymerization temperatures is the increased probability of side reactions such as the dehydration of the diol or the pyrolysis of the ester. Basic catalysts produce less of the undesirable side reactions. 

The reaction is very exothermic. The heat of reaction of propylene oxidation to acrolein is 340.8 kJ /mol (81.5 kcal/mol) the overall reactions generate approximately 837 kJ/mol (200 kcal/mol). The principal side reactions produce acryUc acid, acetaldehyde, acetic acid, carbon monoxide, and carbon dioxide. A variety of other aldehydes and acids are also formed in small amounts. Proprietary processes for acrolein manufacture have been described (25,26). 

Important side reactions are the formation of ether and addition of alcohol to the acrylate to give 3-alkoxypropionates. In addition to high raw material costs, this route is unattractive because of large amounts of sulfuric acid—ammonium sulfate wastes. 

Normally, a slight excess of sulfuric acid is used to bring the reaction to completion. There are, of course, many side reactions involving siHca and other impurity minerals in the rock. Fluorine—silica reactions are especially important as these affect the nature of the calcium sulfate by-product and of fluorine recovery methods. Thermodynamic and kinetic details of the chemistry have been described (34). 

Sulfuric Acid. Generally, sulfuric acid of 93—99% is used. The sulfuric values may be fed to the plant as H2SO4, oleum (20% SO ), or even SO (see Sulfuric acid and sulfur trioxide). Commonly, both H2SO4 and oleum are used. The spHt between the two is determined by water balance. AH water entering the process or produced by side reactions reacts with the SO component of the oleum ... 

In general, an appropriate initiator is a species which has approximately the same stmcture and reactivity as the propagating anionic species, ie, the piC of the conjugate acid of the propagating anion should correspond closely to the piC of the conjugate acid of the initiating species. If the initiator is too reactive, side reactions between the initiator and monomer can occur if the initiator is not reactive enough, then the initiation reaction may be slow or inefficient. 

The vast majority of commercial apphcations of methacryhc acid and its esters stem from their facile free-radical polymerizabiUty (see Initiators, FREE-RADICAl). Solution, suspension, emulsion, and bulk polymerizations have been used to advantage. Although of much less commercial importance, anionic polymerizations of methacrylates have also been extensively studied. Strictiy anhydrous reaction conditions at low temperatures are required to yield high molecular weight polymers in anionic polymerization. Side reactions of the propagating anion at the ester carbonyl are difficult to avoid and lead to polymer branching and inactivation (38—44). 

Propylene-Based Routes. The strong acid-catalyzed carbonylation of propylene [115-07-1] to isobutyric acid (Koch reaction) followed by oxidative dehydration to methacrylic acid has been extensively studied since the 1960s. The principal side reaction in the Koch reaction is the formation of oligomers of propylene. Increasing yields of methacrylic acid in the oxydehydration step is the current focus of research. Isobutyric acid may also be obtained via the oxidation of isobutyraldehyde, which is available from the hydroformylation of propylene. The -butyraldehyde isomer that is formed in the hydroformylation must be separated. 

Centrifugal separators are used in many modem processes to rapidly separate the hydrocarbon and used acid phases. Rapid separation greatly reduces the amounts of nitrated materials in the plant at any given time. After an explosion in a TNT plant (16), decanters (or gravity separators) were replaced with centrifugal separators. In addition, rapid separation allows the hydrocarbon phase to be quickly processed for removal of the dissolved nitric acid, NO, etc. These dissolved materials lead to undesired side reactions. The organic phase generally contains some unreacted hydrocarbons in addition to the nitrated product. 

Manufacture and Processing. Mononitrotoluenes are produced by the nitration of toluene in a manner similar to that described for nitrobenzene. The presence of the methyl group on the aromatic ring faciUtates the nitration of toluene, as compared to that of benzene, and increases the ease of oxidation which results in undesirable by-products. Thus the nitration of toluene generally is carried out at lower temperatures than the nitration of benzene to minimize oxidative side reactions. Because toluene nitrates at a faster rate than benzene, the milder conditions also reduce the formation of dinitrotoluenes. Toluene is less soluble than benzene in the acid phase, thus vigorous agitation of the reaction mixture is necessary to maximize the interfacial area of the two phases and the mass transfer of the reactants. The rate of a typical industrial nitration can be modeled in terms of a fast reaction taking place in a zone in the aqueous phase adjacent to the interface where the reaction is diffusion controlled. 

In addition, however, several minor but important side reactions concurrently proceed with the main reaction. These side reactions may become significant under certain conditions, particularly when the main reaction is slow because of low monomer reactivities or low concentrations. The principal pathways involved in the formation of poly(amic acid) are as shown in Eigure 1. 

Significant quantities of amine and amide esters are formed by side reactions (9). In addition, with dialkanolamines, amide diesters, morpholines, and piperazines can be obtained, depending on the starting material. Reaction of dialkanolamines with fatty acids in a 2 1 ratio, at 140—160°C, produces a second major type of alkanolamide. These products, in contrast to the 1 1 alkanolamides, are water soluble they are complex mixtures of AJ-alkanolamides, amine esters, and diesters, and still contain a considerable amount of unreacted dialkanolamine, accounting for the water solubiUty of the product. Both the 1 1 and the 2 1 alkanolamides are of commercial importance in detergents. 

The concept of functionaUty and its relationship to polymer formation was first advanced by Carothers (15). Flory (16) gready expanded the theoretical consideration and mathematical treatment of polycondensation systems. Thus if a dibasic acid and a diol react to form a polyester, assumiag there is no possibihty of other side reactions to compHcate the issue, only linear polymer molecules are formed. When the reactants are present ia stoichiometric amouats, the average degree of polymerization, follows the equatioa ... 

A troublesome side reaction encountered ia the manufacture and use of amino resias is the conversion of formaldehyde to formic acid. Often the reaction mixture of amino compound and formaldehyde must be heated under alkaline conditions. This favors a Canni22aro reaction ia which two molecules of formaldehyde iateract to yield one molecule of methanol and one of formic acid. 

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