Acid Acetic Hydrobromic

Bromoacetic acid can be prepared by the bromination of acetic acid in the presence of acetic anhydride and a trace of pyridine (55), by the HeU-VoUiard-Zelinsky bromination cataly2ed by phosphoms, and by direct bromination of acetic acid at high temperatures or with hydrogen chloride as catalyst. Other methods of preparation include treatment of chloroacetic acid with hydrobromic acid at elevated temperatures (56), oxidation of ethylene bromide with Aiming nitric acid, hydrolysis of dibromovinyl ether, and air oxidation of bromoacetylene in ethanol. 

Further evidence for a pseudooxazolone intermediate is the fragmentation of 72 by ethyl mercaptan in hydrobromic acid-acetic acid [Eq. (33)]. The mercaptal 74 hydrolyzes readily in acetic acid to give the 2-0X0 acid. 

Hydrobromic instead of hydriodic acid has also been used in quantitative work. Thus Larsson83 evaluated thionyl compounds with a hydrobromic acid/acetic acid reagent, then adding potassium iodide and titrating with thiosulphate. 

Methylation of carbazole phenolic oxygen has been achieved using dimethyl sulfate without reaction at nitrogen. Demethylation of carbazole methyl ethers has been achieved with hydrobromic acid-acetic acid, boron trichloride,and pyridine hydrochloride. Selective demethylation of methoxyl ortho to an aldehydo function has been achieved using boron trifluoride. ° ° Partial demethylation of 1-methoxy-3-formylcarbazole occurred during Wolff-Kischner reduction." ... 

Acetone.—Friedel,4 by electrolyzing a sulphuric-acid solution of acetone, obtained carbonic acid, acetic acid, and formic acid. Mulder 5 and Riche 6 were able to isolate mono- and dichloracetone from the hydrochloric-acid electrolyte, and monobrom,acetone from a hydrobromic-acid solution. 

Chloraniline.—Lob 4 has found that p- arid o-chloraniline are obtained by the electrolytic reduction of nitrobenzene suspended in fuming hydrochloric acid, nitrobenzene dissolved in alcoholic hydrochloric acid, and nitrobenzene dissolved in mixtures of hydrochloric and acetic acids. With hydrobromic acid the corresponding bromanilines are formed. 

There have been known many examples that the hydrogenation of 3p-substituted A5-steroids yields mainly or exclusively saturated steroids of 5a series.166 Lewis and Shoppee studied the influence of various 3 a substituents on the stereochemical course of the hydrogenation of A5-steroids, and found that the 3a substituents lead to the preferential and sometimes exclusive formation of 5P-cholestane derivatives.166 The hydrogenations over platinum oxide were effectuated in methanol or ethyl acetate in the presence of traces of strong acids such as perchloric acid, sulfuric acid or hydrobromic acid. The results summarized by Lewis and Shoppee (eq. 3.34), which also include those by Haworth et al.,167 suggest that the bulkier the axial 3a substituent, the larger is the proportion of 5P steroid formed. The hydrogenation of A4-steroids usually leads to a mixture of 5a and 5P compounds and the stereochemical influence of 3a and 3P substituents is less marked than in the cases of A5-steroids.168... 

Catalytic hydrogenation of the diene (96), from mercuric acetate oxidation of betulin diacetate, yielded (97) and (98). The latter was further reduced to the 18/3H,19/8-lupane (99).70 Isomerization of betulin diacetate with hydrobromic acid in acetic acid-acetic anhydride afforded (97), instead of the usual products with ring E enlarged.71 Glochidone (100) is readily prepared from lupen-3-one by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone.72 73... 

V- Hydrobromic acid, acetic acid, phenyl acetic acid, tris(dimethylamino)-phosphonium hexafluorophosphate vi- Boron hydride dimethylsulfide... 

Many completely aromatic polynuclear hydrocarbons are readily formed by cyclization of aryl-substituted aldehydes, ketones, or related compounds. The simplest case is the formation of naphthalene by refluxing (fi-styrylacetaldehyde, C HsCH = CHCH2CHO, with hydrobromic acid-acetic acid mixture. " The ring closure has found extensive use in the synthesis of 9-alkyl- and 9 aryl-anthracenes and phenanthrenes. " ... 

You now know that HCl and HF are acids because they can donate a hydrogen ion in an acid-base reaction. From their chemical formulas, you can see that each acid can donate only one hydrogen ion per molecule. An acid that can donate only one hydrogen ion is called a monoprotic acid. Other monoprotic acids are perchloric acid (HCIO4), nitric acid (HNO3), hydrobromic acid (HBr), and acetic acid (CH3COOH). The formula for acetic acid is sometimes written HC2H3O2 and the compound is often called ethanoic acid. 

In the steroid series the androstadiendione (29) reacts slowly with 48% hydrobromic acid at room temperature after 5 d the main product (55%) is 1-methylestrone (30) with its isomer (31) in minor amount (11%). The ring bond shifts are inhibited in the 11-ketodienone (32) which essentially reacts exclusively by 1,2-methyl shift in perchloric acid-acetic anhydride to provide the 2-methyl steroid (33), with parallel peracetylation. An 11-hydroxy function has a different effect (see Section 3.5.2.1.2). The 1,2-methyl... 

PPA, phosphorus pentoxide-orthophosphoric acid, acetic anhydride or ethanolic hydrogen chloride may be used to produce this ring in moderate-to-good yields from an acyl- or aroyl-methylthio side-chain of an azole or azine. Heating the ketone with 48% hydrobromic acid gives the same result. A... 

The hydrobromic acid-acetic acid method works well using 33-48% of hydrobromic acid in acetic acid (which can be purchased) with phenol as a bromine scavenger. Phenol is not necessary. The reaction can be carried out at room temperature for an extended period of time, under reflux, refluxed in a sealed tube for an extended period of time, or in a sealed tube at 120°C. Isolation of the product is easier than with the use of concentrated sulfuric acid. Usually, the addition of a large amount of an organic solvent such as ether causes the product to separate as the hydrobromide salt. 

Hydrobromic acid/acetic acid Carboxylic acids from nitriles... 

Hydrobromic acid/acetic acid Dehydration s. 1, 529 HBrlCH,COOH CHC(OH) C C... 

Although strychnine is isomerized, to a limited extent (10%), to isostrychnine by hydrobromic acid-acetic acid mixture, the main product is bromodesoxyisostrychnine (65%), C2iH220N2Br (LXXVI, R = H) (174), while 15% of a more soluble salt is recoverable from the filtrate. A similar reaction occurs with brucine but a simultaneous demethylation leads to bisapomethylbromodesoxyisobrucine (LXXVI, R = OH) (176). Hydrolysis of bromodesoxyisostrychnine by 1 A hydrobromic acid (174) or Letter... 

The desulfuration of 6-unsubstituted-3-methyl-2,3-dihydro-677-l,3,4-thiadiazines 61 (R = Me, Pr ) in boiling glacial acetic acid affords pyrazoles 62 <2003SL2392>. In contrast to the rapid sulfur extrusion of 6-phenyl- or 6-ethoxycarbonyl-6/7-l,3,4-thiadiazines 59 (R = Ph, C02Et) to pyrazoles, a much longer reaction time (40h) was required to achieve a complete desulfuration of 61 (Equation 5). The treatment of 4/7-1,3,4-thiadiazine 63 with concentrated hydrochloric acid or hydrobromic acid (48%) afforded the 5-imino-l,2-dimethylpyrazoles 64 in 40% and 30% yield, respectively (Equation 6). The yield was increased to 53% by the use of glacial acetic acid. The sulfur extrusion proceeded very rapidly and precipitation of considerable amounts of sulfur was observed even after stirring for only 5 min. 

An easy and efficient one pot synthesis of peracetylated glycals from unprotected sugars has been described. In this method the sugar was sequentially treated with acetic anhydride and catalytic hydrobromic acid-acetic acid (to effect per-acetylation), more hydrobromic acid-acetic acid (to form the glycosyl bromide), sodium acetate (to neutralize excess hydrobromic acid) and finally a buffered mixture of sodium acetate, acetic acid, zinc-copper sulfate and water (to effect a reductive-elimination). The method was applied to the syntheses of glycals derived from D-glucose, D-galactose, L-rhamnose, L-arabinose, maltose, lactose and maltotriose. ... 

Hydrobromic acid/acetic acid Partial cleavage of methyl ethers... 

C for periods of up to 6h. In other cases, amides have resisted hydrolysis even during reflux in 48% hydrobromic acid/acetic acid (2). Helmchen el al. [63] reported the directed separation and recovery of acids by neighbouring group assisted hydrolysis. Using amino alcohols as chiral reagents to form amides with the hydroxyl function y or to the carbonyl gave excellent separation factors, and also allowed the hydrolysis to be carried out under somewhat milder conditions, e.g. in 3 M sulphuric acid. 

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