Sulphuric acid, as solvent

The oxidation of sulphoxides containing aromatic groups such as methyl phenyl sulphoxide and diphenyl sulphoxide proceeds at 20-30 °C in low yields in the presence of sulphuric acid as solvent. However the product is usually contaminated with compounds containing nitro groups in the aromatic nucleus, as indicated in equation (6). 

The clearest evidence for microscopic diffusion control in nitration comes from the kinetic studies of Coombes et al. (1968), with low concentrations of nitric acid in 68.3% sulphuric acid as solvent. In this medium, the concentration of nitronium ions is proportional to the concentration of molecular nitric acid as required by (24) and, since the concentration of nitronium ions is very small, the concentration of molecular nitric acid is effectively equal to the stoicheiometric concentration of nitric acid. At a given acidity, the reactions have the kinetic form (25). Nitric acid is written out in full in this equation to show that the rate coefficient is calculated with reference to the stoicheiometric concentration of the acid. This convention assists the comparison of reaction rates over a wide range of acidity. 

The half-life of a base hydrogen-bonded to a strong acid can be very short indeed since proton transfer can occur by tunnelling thus the rate coefficient for proton transfer to water hydrogen-bonded to H30+ has been estimated at 1014 s-1 (Crooks, 1977). For the nitrations in concentrated sulphuric acid as solvent, H2S04 and HSO should take the place of H30+ and H20 in (34) (cf. Cox, 1974). 

Some workers who have used slightly aqueous sulphuric acid as solvent have expressed their results in terms of the van t Hoff i-factor... 

In general, however, the diacetyl derivatives are unstable in the presence of water, undergoing hydrolysis to the mono-acetyl compound, so that when they (or a mixture of mono- and di-acetyl derivatives) are crystallised from an aqueous solvent, e.g., dilute alcohol, only the mono-acetyl derivative is obtained. A further disadvantage of the use of acetic anhydride in the absence of a solvent is that all the impm-ities in the amine are generally present in the reaction product. Heavily substituted amines, t.g., 2 4 6-tribromoaniline, react extremely slowly with acetic anhydride, but in the presence of a few drops of concentrated sulphuric acid as catalyst acetylation occurs rapidly, for example ... 

The commercial polymers are generally resistant to aqueous acids and alkalis although they are attacked by concentrated sulphuric acid. As might be expected of a highly polar polymer it is not dissolved by aliphatic hydrocarbons but solvents include dimethyl formamide and dimethyl acetamide. 

Acetylcyclohexanone. Method A. Place a mixture of 24-6 g. of cyclohexanone (regenerated from the bisulphite compound) and 61 g. (47 5 ml.) of A.R. acetic anhydride in a 500 ml. three-necked flask, fitted with an efficient sealed stirrer, a gas inlet tube reaching to within 1-2 cm. of the surface of the liquid combined with a thermometer immersed in the liquid (compare Fig. II, 7, 12, 6), and (in the third neck) a gas outlet tube leading to an alkali or water trap (Fig. II, 8, 1). Immerse the flask in a bath of Dry Ice - acetone, stir the mixture vigorously and pass commercial boron trifluoride (via an empty wash bottle and then through 95 per cent, sulphuric acid) as fast as possible (10-20 minutes) until the mixture, kept at 0-10°, is saturated (copious evolution of white fumes when the outlet tube is disconnected from the trap). Replace the Dry Ice-acetone bath by an ice bath and pass the gas in at a slower rate to ensure maximum absorption. Stir for 3 6 hours whilst allowing the ice bath to attain room temperature slowly. Pour the reaction mixture into a solution of 136 g. of hydrated sodium acetate in 250 ml. of water, reflux for 60 minutes (or until the boron fluoride complexes are hydrolysed), cool in ice and extract with three 50 ml. portions of petroleum ether, b.p. 40-60° (1), wash the combined extracts free of acid with sodium bicarbonate solution, dry over anhydrous calcium sulphate, remove the solvent by... 

Compounds of sulphur(II) undergo the expected oxidations with DIB thiols to disulphides and sulphides to sulphoxides. Thiols form initially unstable iodine(III) intermediates which react with alkynes (Section 3.7). With some sulphides, DIB proved to be uniquely efficient, for example in the oxidation of thioxanthone [132]. The best conditions for high yields involved the use of acetic acid as solvent and catalytic amounts of sulphuric acid no heating was required and the reaction was completed in about 5 minutes [133]. 

According to Ridd [79] the clearest evidence for microscopic diffusion control in nitration comes from the kinetic studies of Coombes, Moodie and Schofield [80] with low concentration of nitric acid in 68.3% sulphuric acid as a solvent. In this medium the concentration of nitronium ions is proportional to the concentration of molecular nitric acid according to equation (27) ... 

Catalytic hydrogenation of (193) in sulphuric acid solution gives mainly (+)-6, 7 -dihydropycnanthine, which is identical with pleiomutinine (194, see ref. 113), and small amounts of 6, 7, 8, 9 -tetrahydro-8, 9 -diano-pycnanthine (198) the latter is the major product on hydrogenation in ethyl acetate in the presence of potassium carbonate. With methanol-acetic acid as solvent (194), (198), and the N(h-)-methyl derivative of (198), namely (199), are obtained. All three hydrogenation products exhibit the same u.v. spectrum as pycnanthine (193). Product (198) contains a secondary amine function (acetylation) (194) cannot be further hydrogenated to (198) or (199). 

Ingold and his co-workers( ) proposed and firmly established a scheme now generally accepted for the mechanism of aromatic nitration with nitric acid or mixed nitric and sulphuric acids as nitrating agents, typically, in homogeneous solution in an organic solvent. In this the nitronium ion, NO2, is the active intermediate which reacts with the aromatic compound, ArH -... 

A similar non-aqueous process has been decribed using iso-octyl phosphoric acid, monododecyl phosphoric acid or monoheptadecyl phosphoric acid as solvents, none of which require the ammonium nitrate addition. Methyl ethyl ketone, other ketones, or kerosene are suitable diluents. The sulphuric acid usage is much less than that normally required for, for example, a dilute acid leach of the camotite ore used, since the high proportion of lime present in the ore is not taken into solution. Hydrochloric acid is preferable for backwashing the uranium. 

E. Kolvari, M. A. Zolfigol, N. Koukabi, B. Shirmardi-Shaghasemi, Chem. Pap. 2011, 65, 898-902. A simple and efficient one-pot synthesis of Hantzsch 1,4-dihydropyridines using silica sulphuric acid as a heterogeneous and reusable catalyst under solvent-free conditions. 

Reduce a sufficient quantity to a No. 60 powder and extract 25 g of the powder, in two separate portions, each of 12-5 g, by the B.P. method given above, increasing all quantities of solvent by 25 per cent. Combine the final chloroform extracts, evaporate to low volume and then dilute to exactly 50 ml with chloroform and mix. Pipette 20 ml of this solution into a shallow, open dish, evaporate to dryness and titrate the alkaloids with 0 05N sulphuric acid as in the B.P. assay. Dilute the titrated liquid to about 35 ml with water, add 10 ml of 2N sodium hydroxide and evaporate for fifteen minutes on a water-bath. Cool, neutralise with dilute hydrochloric acid and add 0 05 ml of the acid in excess. Transfer to a separator and extract, first wdth four 25-ml portions and then with two 20-ml portions of a mixture of 1 volume of / opropyl alcohol and 3 volumes of chloroform, washing each extract with the same 15 ml of water. Combine the extracts, evaporate the solvent and dissolve the residue in 15 ml of w arm water. Cool the soluticm and titrate with 0-02N sodium liydroxidc using phenolphthalein as indicator. 

Dissolve 10 discs in N sulphuric acid and make up to 250 ml. Dilute 10 ml of this solution to 100 ml with the same solvent. Measure the maximum extinction of a 1 -cm layer at about 234 mfjL using the N sulphuric acid as blank. Calculate the amount of cocaine in each disc. 

Cocking used ether for extraction of the purified balsamic acids and this solvent is preferable. Further, the B,P, directs the mixed benzoic and cinnamic acids to be titrated but they should be weighed after drying in zacuo over sulphuric acid as they are present in variable proportions the amount of cinnamic acid present may be determined by bromination,... 

Many LCPs are virtually unaffected by most chemicals and solvents over a broad temperature range. Exposure to such aggressive chemicals as formic acid and sulphuric acid, and solvents such as methylene chloride, trichloroethane and Fluorinert FC-70 starting at room temperature and ranging, in some cases, up to 225 °C yields no significant changes in properties, dimensions or weight. Tables 7.9 and 7.10 illustrate representative chemical-resistance data. 

Made by esterification of pure cellulose with acetic acid and sulphuric acid as catalyst in solvents of medium polarity. This produces readily soluble resins with varying acetate content depending on the process. The polymers are processible by injection moulding, extrusion and blow moulding. Principle cellulose polymers are cellulose acetate (CA), cellulose acetobutyrate (CAB) and cellulose propionate (CP). Ethyl cellulose forms the other group of polymers. Applications are limited by environmental and chemical stability. 

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