Sulfuric acid solvent, esterification

Acid—Base Chemistry. Acetic acid dissociates in water, pK = 4.76 at 25°C. It is a mild acid which can be used for analysis of bases too weak to detect in water (26). It readily neutralizes the ordinary hydroxides of the alkaU metals and the alkaline earths to form the corresponding acetates. When the cmde material pyroligneous acid is neutralized with limestone or magnesia the commercial acetate of lime or acetate of magnesia is obtained (7). Acetic acid accepts protons only from the strongest acids such as nitric acid and sulfuric acid. Other acids exhibit very powerful, superacid properties in acetic acid solutions and are thus useful catalysts for esterifications of olefins and alcohols (27). Nitrations conducted in acetic acid solvent are effected because of the formation of the nitronium ion, NO Hexamethylenetetramine [100-97-0] may be nitrated in acetic acid solvent to yield the explosive cycl o trim ethyl en etrin itram in e [121 -82-4] also known as cyclonit or RDX. 

Direct, acid catalyzed esterification of acryhc acid is the main route for the manufacture of higher alkyl esters. The most important higher alkyl acrylate is 2-ethyIhexyi acrylate prepared from the available 0x0 alcohol 2-ethyl-1-hexanol (see Alcohols, higher aliphatic). The most common catalysts are sulfuric or toluenesulfonic acid and sulfonic acid functional cation-exchange resins. Solvents are used as entraining agents for the removal of water of reaction. The product is washed with base to remove unreacted acryhc acid and catalyst and then purified by distillation. The esters are obtained in 80—90% yield and in exceUent purity. 

Chemical Properties. MSA combines high acid strength with low molecular weight. Its pK (laser Raman spectroscopy) is —1.9, about twice the acid strength of HCl and half the strength of sulfuric acid. MSA finds use as catalyst for esterification, alkylation, and in the polymerisation and curing of coatings (402,404,405). The anhydrous acid is also usefijl as a solvent. 

Other examples of esterification with trialkyloxonium salts have been reported.7,8 The present procedure offers the advantages that the reactive carboxylate ion is generated in sitv and that a low-boiling, nonaqueous solvent is employed, whereby the experimental procedure is considerably simplified. A related method has been reported which utilizes a hindered amine wdth dimethyl sulfate [Sulfuric acid, dimethyl csterj as the alkylating agent.9 The present procedure is carried out under somewhat milder conditions and avoids the use of highly toxic reagents. 

Ethyl 4-ctmino-3-nitrobenzoate mp 136° Insol in peer eth, sol in usual org solvents may be prepd by refluxing ethyl 4-bromo-3-nitrobenzoate and ale NH3 at 150° for 3 hrs by esterification of 4-amino 3 nitrobenzoic acid with abs ale in sulfuric acid or by refluxing ethyl 4 ethoxy-3-... 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

The final oxidation step of the primary alcohol at C-l in L-Srb requires acetone protection, which is carried out in a standard textbook way in the presence of an excess of sulfuric acid. The oxidation at C-l has been accomplished in a number of ways [147] it seems that nowadays aerobic oxidation in the presence of palladium or platinum is preferred. Deprotection, requiring additional sulfuric acid, affords 2KLG, which is transformed into ASA via esterification and lac-tonization. Alternatively, the diacetone derivative of 2KLG can be converted directly into ASA by treatment with HC1 in an organic solvent. 

Esterification is usually effected by refluxing the acid and alcohol with a small amount of sulfuric acid, hydrogen chloride, or arylsulfonic acid. The equilibrium is shifted to the right by an excess of one of the reactants or by removal of water either by azeotropic distillation or by means of a suitable drying agent. The necessity for continuous drying is eliminated when methylene or ethylene chlorides are used as solvents for the reaction. A small amount of an acid chloride such as thionyl chloride, acetyl chloride, or stearoyl chloride has proved superior to hydrogen chloride as a catalyst for certain esterifications at room temperature. ... 

HPA is very soluble in oxygen-containing polar solvents such as water, alcohol, ether, and ketone. In these polar solvents, HPA works as an efficient acid catalyst for alkene hydration, the Prins reaction, nucleophilic cleavage of alicyclic and cyclic ethers, esterification, hydrolysis, transesterification, and acetalization. The catalytic activity of HPA in these reactions is much higher than that of ordinary protonic acids such as sulfuric acid and p-toluenesulfonic acid, and the activation energies of the HPA-catalyzed reactions are remarkably reduced, owing to stabilization of the cationic reaction intermediates by the heteropoly anion [1,4]. 

Dimethyl terephthalate is obtained by the esterification of terephthalic acid by methanol. Terephthalic acid is a high-melting (above 3Q0°C), insoluble material and requires special conditions for esterification. Two parts of methyl alcohol, 1 part of terephtiialic add, and 0.01 part of sulfuric acid are placed in a closed, a tated pr sure vessel and heated to 150°C for 2-3 hr. During the last hour, 5-6 parts of additional methyl alcohol is added slowly to the liquid reactants and distOled to remove the water of reaction. By cooling, the dimethyl terephthalate is completely separated from the solution. Yields run high, as 95 per cent. The dimethyl terephthalate can be purified by crystallization from high-boiling solvents, such as xylene, or it may be distilled. 

Gas chromatography (GC) analysis involving simultaneous solvent extraction and hydrolytic esterification of PHA is generally carried out for the determination of intracellular PHA content (Braunegg et al. 1978). GC analysis with propanoly-sis in hydrochloric acid rather than acidic methanolysis in sulfuric acid was also reported (Riis and Mai 1988). 

Acid-catalysed esterification reactions in ILs have been extensively studied, and will be the main focus of this section. In 2001, Deng et al. first reported the synthesis of allq l acetate esters in an IL with concentrated sulfuric acid as the acid catalyst (Scheme 3.7). The majority of subsequent studies, however, have switched away from an IL with an added acid catalyst and towards Bronsted acid ionic liquids (BAILs) - a type of task-specific ionic liquid. BAILS incorporate an acidic moiety (typically either a sulfonic acid or a protonated nitrogen) on the cation allowing the BAILS to have dual functionality as both a solvent and a catalyst. There are several different classes of BAILs that have been applied to esterifications such as imidazo-lium 1, imidazolium sulfonic 2, phosphonium sulfonic 3, pyridinium sulfonic 4, quaternary ammonium 5, quaternary ammonium sulfonic 6 and lactam 7 based-BAILs (Scheme 3.8). 

LA can be purified either by precipitation of metal lactates followed by a neutralizing reaction with sulfuric acid [8] or by esterification with alcohol, distillation and hydrolysis of the formed ester, or by electro-dialysis. A more recent purification process is to extract LA by liquid-liquid extraction making use of at least one organic solvent not miscible with water in the presence or not of at least one Lewis base such as a ternary amine for instance. With this process, lactic acid must be recovered in a second step with a liquid-liquid back-extraction. This step allows to re-transfer the lactic acid to water. Finally, LA in acid- and/or ammonium lactate or metal lactate-form may be purified by processing it on cationic and/or anionic ion-exchange columns. 

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