Acetals acidic conditions

Fig. 9. Conjoint Liquid Chromatography (CLC). Separation of proteins from mouse ascites and isolation of monoclonal antibody IgG in one step obtained by a combination of CIM QA and CIM Protein A Disks. Conditions Separation mode CLC (first disk CIM QA, 12 x 3 mm ID, 0.34 ml second disk - CIM Protein A, 12 x 3 mm ID, 0.34 ml, inserted in monolithic column housing) Instrumentation Gradient HPLC system with extra low dead volume mixing chamber Sample Mouse ascites Injection volume 20 pL Mobile Phase Buffer A 20 mM Tris-HCl, pH 7.4 Buffer B Buffer A + 1 M NaCl Buffer C 0.1 M Acetic acid Conditions Gradient 0 - 50 % B in 50 s, 100% A for 40 s, 100% C for 30 s Flow Rate 4 ml/min Detection UV at 280 nm... 

Oxidative expansion of a fl-lactam.2 Treatment of the penicillinate 1 with KMn04 in aqueous acetic acid (conditions usually resulting in oxidation of the S to — S02—) provides 2 in 56% yield. 

Condensation of benzoylacetone with (222) in acetic acid did not form (223) but rather (224). Compound (223) is most certainly formed in this process since a customary method for preparing the [l,2,3]triazoIo[l,5-a]pyrimidine molecule was used however, upon formation, (223) rearranged to (224) under the acetic acid conditions (Scheme 13) (71JCS(C)2156). 

The target molecule contains an imidazolinone off of the C4, Cg positions. This heterocycle can be formed by adding a molecule of urea to an alpha-bromoketone. Accordingly, intermediate 18 would be brominated with a radical process using Nbromosuccinimide in methylene chloride,25 then urea would be added under acetic acid conditions to give the new heterocycle. Ammonium acetate in acetic acid would then complete the hexacyclic intermediate 21. ... 

Despite these other reduction methods—notably the excellent Cava variation [16]—the traditional iron/acetic acid and catalytic hydrogenation conditions continue to be preferred. Eor example, the indoles 9-22 were prepared using the iron/acetic acid conditions (Scheme 3 [19-32]). Indole 10 was converted to 5-hydroxytryptamine-4,7-dione, the neurocytotoxic product of 5,7-dihydroxy-tryptamine [20], and indoles 11 and 12 were recruited for... 

In our subsequent search for the conditions leading to the mild and selective formation of the B-ring, we were able to explore the pyrrolidine acetate-promoted reaction that is most likely to proceed through the formation of enamine (30) and results in monocyclized aldol condensation product 29a-e (Scheme 15). When subjected to pyrrolidine/acetic acid conditions, substrates 14 were selectively monocyclized to the corresponding enones 29a-e in good yield and with no erosion in enantiomeric excess. In addition to substrates 29a-c, this protocol provided access to functionalized Wieland-Mischer and Hajos-Parrish ketones 29d and 29e, which cannot be... 

The Duff reaction is a formylation method normally used for electron-rich aromatics such as phenols and aromatic amines with the formylating agent being hexamethylenetetramine in the presence of glycerol or acetic acid. Conditions are rigorous and the yields are generally low, but the main value is the occurrence of mainly... 

Actually the optimum pH for the invertase reaction is about 4-8, and under these conditions the reaction proceeds even more rapidly. The solution can be adjusted approximately to this pH by adding 6 ml. of 1% acetic acid at the beginning of the experiment. 

It is a well-known fact that substances like water and acetic acid can be cooled below the freezing point in this condition they are said to be supercooled (compare supersaturated solution). Such supercooled substances have vapour pressures which change in a normal manner with temperature the vapour pressure curve is represented by the dotted line ML —a continuation of ML. The curve ML lies above the vapour pressure curve of the solid and it is apparent that the vapour pressure of the supersaturated liquid is greater than that of the solid. The supercooled liquid is in a condition of metastabUity. As soon as crystallisation sets in, the temperature rises to the true freezing or melting point. It will be observed that no dotted continuation of the vapour pressure curve of the solid is shown this would mean a suspended transformation in the change from the solid to the liquid state. Such a change has not been observed nor is it theoretically possible. 

Small quantities of the sjunmetrical ketones (CHjjjCO and (CHjCHjCHjjjCO (di-n-propyl ketone) are formed as by-products these can easily be removed by fractional distillation through an efficient column. An excess of the cheaper reagent, acetic acid, is employed the resulting acetone is readily removed by washing with water and little di-n-propyl ketone is formed under these conditions. 

Diphenic acid. Phenanthrene upon oxidation in acetic acid solution at 85° with 30 per cent, hydrogen peroxide gives diphenic acid (diphenyl-2 2 -di-carboxyHc acid) no phenanthraquinone is formed under these experimental conditions. The reaction is essentially an oxidation of phenanthrene with peracetic acid. (For another method of preparation, see Section I V,74.)... 

Lead dioxide in acetic acid solution gives lead tetra acetate which oxidises hydrogen bromide (and also hydrogen iodide), but has practically no cflFect under the above experimental conditions upon hydrogen chloride. 

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

Synthesis The synthesis uses rather more vigorous conditions than those which gave the p-hydroxy carbonyl compoimds. In fact tBull. Chem. Japan. 1952, 25, 54, Chem. Abs..l954. 48. 5143) you can either treat the p-hydroxy compoimd with HCl in acetic acid or do the condensation in base ... 

The catalysed nitration of phenol gives chiefly 0- and />-nitrophenol, (< 0-1% of w-nitrophenol is formed), with small quantities of dinitrated compound and condensed products. The ortho para ratio is very dependent on the conditions of reaction and the concentration of nitrous acid. Thus, in aqueous solution containing sulphuric acid (i 75 mol 1 ) and nitric acid (0-5 mol 1 ), the proportion of oriha-substitution decreases from 73 % to 9 % as the concentration of nitrous acid is varied from o-i mol l i. However, when acetic acid is the solvent the proportion of ortAo-substitution changes from 44 % to 74 % on the introduction of dinitrogen tetroxide (4-5 mol 1 ). 

The kinetics of nitration of anisole in solutions of nitric acid in acetic acid were complicated, for both autocatalysis and autoretardation could be observed under suitable conditions. However, it was concluded from these results that two mechanisms of nitration were operating, namely the general mechanism involving the nitronium ion and the reaction catalysed by nitrous acid. It was not possible to isolate these mechanisms completely, although by varying the conditions either could be made dominant. 

Chloroanisole and p-nitrophenol, the nitrations of which are susceptible to positive catalysis by nitrous acid, but from which the products are not prone to the oxidation which leads to autocatalysis, were the subjects of a more detailed investigation. With high concentrations of nitric acid and low concentrations of nitrous acid in acetic acid, jp-chloroanisole underwent nitration according to a zeroth-order rate law. The rate was repressed by the addition of a small concentration of nitrous acid according to the usual law rate = AQ(n-a[HN02]atoioh) -The nitration of p-nitrophenol under comparable conditions did not accord to a simple kinetic law, but nitrous acid was shown to anticatalyse the reaction. 

The observation of nitration at a rate independent of the concentration and the nature of the aromatic means only that the effective nitrating species is formed slowly in a step which does not involve the aromatic. The fact that the rates of zeroth-order nitration under comparable conditions in solutions of nitric acid in acetic acid, sulpholan and nitromethane differed by at most a factor of 50 indicated that the slow step in these three cases was the same, and that the solvents had no chemical involvement in this step. The dissimilarity in the rate between these three cases and nitration with acetyl nitrate in acetic anhydride argues against a common mechanism, and indeed it is not required from evidence about zeroth-order rates alone that in the latter solutions the slow step should involve the formation of the nitronium ion. 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

Six protective groups for alcohols, which may be removed successively and selectively, have been listed by E.J. Corey (1972B). A hypothetical hexahydroxy compound with hydroxy groups 1 to 6 protected as (1) acetate, (2) 2,2,2-trichloroethyl carbonate, (3) benzyl ether, (4) dimethyl-t-butylsilyl ether, (5) 2-tetrahydropyranyl ether, and (6) methyl ether may be unmasked in that order by the reagents (1) KjCO, or NH, in CHjOH, (2) Zn in CHjOH or AcOH, (3) over Pd, (4) F", (5) wet acetic acid, and (6) BBrj. The groups may also be exposed to the same reagents in the order A 5, 2, 1, 3, 6. The (4-methoxyphenyl)methyl group (=MPM = p-methoxybenzyl, PMB) can be oxidized to a benzaldehyde derivative and thereby be removed at room temperature under neutral conditions (Y- Oikawa, 1982 R. Johansson, 1984 T. Fukuyama, 1985). 

Unsymmetrically substituted dipyrromethanes are obtained from n-unsubstitued pyrroles and fl(-(bromomethyl)pyiToIes in hot acetic acid within a few minutes. These reaction conditions are relatively mild and the o-unsubstituted pyrrole may even bear an electron withdrawing carboxylic ester function. It is still sufficiently nucleophilic to substitute bromine or acetoxy groups on an a-pyrrolic methyl group. Hetero atoms in this position are extremely reactive leaving groups since the a-pyrrolylmethenium( = azafulvenium ) cation formed as an intermediate is highly resonance-stabilized. 

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