Acetic-sulfuric acid solutions

Nuclear magnetic resonance spectrometry has solved so many problems that one would hope it could be applied to the determination of aliphatic weak bases. Taft and Levins (338) have succeeded in using this method through the effect of protonation on the fluorine resonance of several p-fluorinated bases. Unfortunately, the flu-orinated aromatic system is required and also a relatively concentrated solution of indicator so that the use of aqueous acid is ruled out. In acetic-sulfuric acid solutions Taft finds serious medium effects for Hammett indicators but sharp titration curves for car-bonium ion bases. This result is in complete agreement with the conclusions described previously (II-D) for solvation of carbonium ions compared to other onium ions. 

Isoxazole was first synthesized by Claisen in 1903 from propargylaldehyde diethyl acetal and hydroxylamine (03CB3664). It has also been obtained by addition of fulminic acid to acetylene in methanol-dilute sulfuric acid solution, by acidic hydrolysis of 5-acetoxyisoxazo-line, by reaction of /S-chloroacrolein or/3-alkoxyacrolein with hydroxylamine hydrochloride... 

The bromination of 7-methoxy-l-methyl-j8-carboline (harmine) was studied by Fischer. He obtained a compound, Ci3Hi2Br4N20, which he called tetrabromoharmine, by the action of bromine water on a dilute sulfuric acid solution of harmine. The bromination of harmine was reinvestigated by Hasenfratz, who found that two products (both hydrobromides) could be isolated when harmine was treated with bromine in aqueous acetic acid. The major component formed colorless needles and was called bromoharmine hydrobromide (free base colorless needles, m.p. 275°), while the product obtained in lesser amount was a canary-yellow dihydrate which was named isobromoharmine hydrobromide (free base colorless needles, m.p. 

Preparation of 2-Hydroxy-4,4 -Dicyanostilbene 10 grams of 2-amino-4,4 -dicyanostilbene thus prepared were dissolved in 400 cc of boiling glacial acetic acid and 200 cc of dilute sulfuric acid added the solution was suddenly chilled and diazotized over one and a half hours at 5° to 10°C with sodium nitrate (3.0 grams/15 cc H O). The diazonium salt solution was decomposed by boiling for 15 minutes with 600 cc of 55% aqueous sulfuric acid solution the solution was diluted, cooled and filtered. The residue crystallized from ethyl alcohol as lemon yellow prismatic needles, MP 296°C. 

At the end of the 24-hour period, the ethanol is removed under reduced pressure on a steam bath. A 2N sulfuric acid solution (2 1.) is added to the warm residue, and the mixture is stirred vigorously for 3—4 hours (Note 3). The solid is removed by suction filtration and washed several times with water. The air-dried product is a pale-bufi powder weighing 180-190 g., m.p. 126-128°. The solid is added to 1.5 1. of ethyl acetate, the mix-... 

Herrero and Abruna [25] have also studied the kinetics and mechanism of Hg UPD on Au(lll) electrodes in the presence and absence of bisulfate, chloride, and acetate ions. In the absence of the interacting anions (in perchloric acid), the Hg UPD was significantly controlled by gold-mercury surface interactions. In sulfuric acid solutions, the kinetics of the initial and final stages of mercury deposi-tion/dissolution was altered. The presence of two well-ordered structures at potentials below and above mercury deposition led to the formation of two pairs of sharp spikes in cyclic voltammograms. In the chloride medium, the voltammetric profile exhibited two sharp peaks and thus it was very similar to that obtained in sulfuric acid solution. Neither nucleation, nor growth kinetics mechanism was found to be linked to the process of formation/disruption of the mercury chloride adlayer. The transients obviously deviated from the ideal Langmuir behavior. 

The hydration of acetylene produces acetaldehyde which then can be converted to acetic acid and other derivatives. The process is similar to olefin hydration employing a sulfuric acid solution containing also a mercurous sulfate catalyst. 

In a comparable solution of benzoic acid the freezing point is depressed only twice the predicted amount, indicating only a normal acid-base reaction. Further, a sulfuric acid solution of methyl mesitoate when poured into water gave mesitoic acid, while a similar solution of methyl benzoate similarly treated did not.534 The AacI mechanism is also found when acetates of phenols or of primary alcohols are hydrolyzed in concentrated (more than 90%) H2SO4 (the mechanism under the more usual dilute acid conditions is the normal Aac2).535... 

A freshly prepared solution of nitroguanidine in concentrated sulfuric acid contains no nitric acid, for none can be distilled out of it, but it is ready to produce nitric acid (by the hydration of the nitroamide) if some material is present which will react with it. Thus, it gives up its nitro group quantitatively in the nitrometer, and it is a reagent for the nitration of such substances as aniline, phenol, acet-p-toluide, and cinnamic acid which are conveniently nitrated in sulfuric acid solution. 

In sulfuric acid solutions alone, the formation of an insoluble layer of the sulfate on the electrode surface may serve to inhibit the rapid bulk corrosion which has been observed in the presence of acetic acid. 

The nitrosation of phenol and cresols in buffer solutions involves a diffusion-controlled C-nitrosation followed by rate-limiting proton loss. /r-Crcsol is much less reactive than the other substrates.79 Nitrosation in trifluoroacetic acid or in acetic-sulfuric acid mixtures is regioselective (e.g. 4-nitroso-m-xylene is fonned from m-xylene) and possible non-selective nitrous acid-catalysed nitration can be eliminated by purging reaction solutions with nitric oxide.80... 

Finch and Symons,87 on reinvestigation of the absorption of aliphatic alcohols and alkenes in sulfuric acid solution, showed that the condensation products formed with acetic acid (used as solvent for the precursor alcohols and alkenes) were responsible for the spectra and not the simple alkyl cations. Moreover, protonated mesityl oxide was identified as the absorbing species in the system of isobutylene, acetic acid, and sulfuric acid. 

There are many methods for effecting the nitration of aromatic compounds. Reactive compounds, for example, phenol, will nitrate in dilute nitric acid, but usually more vigorous reaction conditions consisting of nitric acid (either concentrated or fuming) or nitrate salts in sulfuric acid are used. Solutions of nitric acid in other mineral acids, e.g., perchloric or phosphoric acid, have sometimes been used and can give nitro products in isomeric proportions different from those found in sulfuric acid solution. Nitric acid inorganic solvents, particularly acetic acid or acetic anhydride, has also been used frequently. In acetic anhydride acetyl nitrate rather than the nitronium ion is usually the reacting species. 

The flask containing the solution of the (+)-(3aS,7aS)-2,3,3a,4,7,7a-hexahydro-3a-hydroxy-7a-methyl-lH-indene-1,5(6H)-dione in N,N-dimethyl -formamide is placed 1n an oil bath and heated to 95°C. When the temperature reaches 70-75°C, an 18.8-mL aliquot of the coned sulfuric acid in N,N-dimethylformamide solution is added in one portion. The reaction mixture is heated to 95°C for 3.0 hr. After 1.0 hr, an additional 7.5-mL aliquot of the coned sulfuric acid in N,N-dimethy1formamide solution is added in one portion. The reaction is monitored for completeness by GLC (Note 15) and cooled. The solvent is removed on a rotary evaporator at 45°C (0.3-0.5 ran) to give a brown oil. The material is taken up in 375 mL of dlchloromethane. The solution is washed with two 190-mL portions of 2.0 N sulfuric acid solution which have been saturated with sodium chloride, two 190-mL portions of saturated sodium bicarbonate solution which have been saturated with sodium chloride and 190 mL of saturated brine. Each aqueous wash is extracted, in turn, with the same two 190-mL portions of dichloromethane. The combined dichloromethane solutions are dried over sodium sulfate, filtered, and the solvent is removed on a rotary evaporator at 40°C (70 mm) to give 38.8-39.6 g of oily, brown semisolid. This material is taken up in 78 mL of ethyl acetate and the solution is applied to a dry column of 78 g of silica gel (Note 16). The column is eluted with 600 mL of ethyl acetate and the total eluate is... 

In addition, substances which are easily sulfonated, hydrolyzed, or otherwise changed, by concentrated sulfuric acid cannot be nitrated in sulfuric acid solution. In these circumstances it is necessary either to use aqueous nitric acid of suitable concentration, or to carry out the nitration with concentrated nitric acid in a solution or suspension in an organic liquid. The organic liquid must be one which is affected as little as possible by nitric acid under the conditions prevailing in the process (for example, glacial acetic acid, nitrobenzene, or o-dichlorobenzene). 

Sulfuric or phosphoricacids are used for the ketonic hydrolysis, as in the preparation of methyl n-amyl ketone. Also, the hydrolysis is brought about by boiling with acetic-sulfuric acid mixture, hot 5% potassium hydroxide solution, or hydriodic acid if the hydrolysis is especially difficult. Benzyl ace tone, QH, CHjCHjCOCH, is formed by hydrolysis of the corresponding /8-keto ester with water at 150-250° and 200 atm. Diaikylated /S-keto esters are stable to this treatment therefore, a single ketone can be obtained from a mixture of mono- and di-alkylated /3-keto esters. ... 

Diazotization of 2-aminopyrazine with nitrous acid in dilute or concentrated sulfuric acid gave 2 hydroxypyrazine (to 67% yield) (86, 477, 720, 818). Many such conversions have been described, mostly using nitrosylsulfuric acid in concentrated sulfuric acid solution. Preparations of hydroxypyrazines from the aminopyrazines are summarized as follows 2-hydroxy-3-methylpyrazine (sodium nitrite in concentrated sulfuric acid-acetic acid) (681), 2Jiydroxy-3,5-dimethylpyrazine (aqueous nitrous acid, then at 60°) (524), 3-hydroxy-2,5-dimethylpyrazine (477), 2,5-diethyl-3-hydroxypyrazine (aqueous nitrous acid) (478), 2-hydroxy-6-phenyl-pyrazine (365a), 24iydroxy-3,5-diphenylpyrazine (nitrous acid in N hydrochloric acid) (524), 3-hydroxy-2,5-diphenylpyrazine (282), 2-s-butyl-3-hydroxy-5-isobutyl-pyrazine (93), 5TS-butyl-3 hydroxy-2-isobutylpyrazine (92, 536), 2,5-di-s-butyl-3-hydroxypyrazine (89, 720), 3-hydroxy-2-isobutyl-5-isopropylpyrazine (103, 525), 2,3-dihydroxypyrazine (from 2 amino-3-hydroxypyrazine) (757, 1055) and its... 

---