Perchloric acid amides

The classical method for tert-butyl esterification involves nnineral add catalyzed addition of the amino acid to isobutene. Both, N-protected, e.g. Z-Xaa-OH, and unprotected amino acids form tert-butyl esters with isobutene in the presence of catalytic amounts of sulfuric acid or TosOH. " Another efficient method is the transesterification of an acetic acid tert-bvXy ester catalyzed by perchloric acid. " Amide tert-butylation was recognized as a side reaction in the presence of perchloric acid, but could be completely suppressed by using sulfuric acid. Both methods, acid-catalyzed addition to isobutene and the transesterification of acetic add terf-butyl esters, result in simultaneous terf-butyl-ation of hydroxy and sulfanyl groups. A synthetic route to Z-Thr-OtBu, Z-Ser-OtBu, and Z-Hyp-OtBu without conconnitant O-alkylation involves the hydroxy protection by the acetoacetyl group, which is readily cleaved by treatment with 2 equivalents of hydrazine in EtOH for 30 minutes. ... 

When C1207 reacted with NC13, primary and secondary amine compounds belonging to the class of perchloric acid amides were produced ... 

Amides can be titrated direcdy by perchloric acid ia a nonaqueous solvent (60,61) and by potentiometric titration (62), which gives the sum of amide and amine salts. Infrared spectroscopy has been used to characterize fatty acid amides (63). Mass spectroscopy has been able to iadicate the position of the unsaturation ia unsaturated fatty amides (64). Typical specifications of some primary fatty acid amides and properties of bisamides are shown ia Tables 5 and 6. 

After cooling and dilution with methyl-Cellosolve (2-methoxyethanol), acetic anhydride is slowly added (in order to convert the secondary amine to amide) and the solution is cooled to room temperature. Finally, the resulting tertiary amine, representing the original unsaturate, is titrated with 0.5 N perchloric acid in methyl-Cellosolve, either visually (with thymol blue + xylene cyanol... 

Fig. 5 Excess acidity plots according to equation (17) for three amides in aqueous perchloric acid at 45°C (upper lines) and 15°C (lower lines). Open circles, 4-methoxy-benzamide closed circles, 3,4,5-trimethoxybenzamide open triangles, 3-nitrobenzamide. Data from ref. 64 numbers to the right of the dashed lines are log/values.

Table 10 p bh+ values, m slopes, enthalpies and entropies of ionization for some amides in aqueous perchloric acid."... 

O-Protonated cations of eimides in concentrated and anhydrous acids are now well characterized by nmr spectroscopy. O-Protonated cations of N,N-dimethyl amides are most easily observed, even in 72% perchloric acid which has a water activity of about 10 , because for tertiary amides the N-protonated forms is relatively less stabilized by hydration (Liler, 1972a). O-Protonated cations of N-alkyl amides show considerable exchange of NH-protons with the solvent in 72% perchloric acid owing to the intervention of the N-protonated form. For primary amides (acetamide), however, O-protonated cations are not observable in that solvent (Liler, 1972b),... 

The failure of the acidity function approach is shown in the work of Leisten212, who studied the rates of hydrolysis of the thirteen amides listed in Table 27 in 5.9, 7.2 and 8.5 M perchloric acid. If the mechanism of hydrolysis is of the A-2 type213, where a rapid reversible initial protonation of the amide is followed by the attack of water on to the conjugate acid, then the Ziicker-Hammett hypothesis214 would predict that the rates of hydrolysis in solutions of different acidity should be proportional to the acid concentration. Therefore, kx (the rate coefficient for the attack of water onto the conjugate acid) should be proportional to [H30+ ] lh0. In Table 27 the values of the first-order coefficients for hydrolysis at 5.86 and 7.19 M HC104 are given and compared with the calculated value. 

FIRST-ORDER RATE COEFFICIENTS FOR THE HYDROLYSES OF AMIDES IN AQUEOUS PERCHLORIC ACID SOLUTIONS AT 95°C WITH THE CALCULATED AND OBSERVED RATIOS FOR THE RATES AT TWO... 

Dialkylaminofurans (169) are prepared from tertiary amides of /3-aroylpropionic acids (167), which on treatment with acetic anhydride and perchloric acid yield 2,3-dihydrofuran-2-furylideneammonium salts (168) from which stable dialkylaminofurans. (169) can be obtained. Dilute acid hydrolysis gives the butenolides (170) (73JCS(P1)2523). 

The usual routes to 1,3-oxazinium salts consist of 1,4-cycloadditions between either a,/3-unsaturated /3-chlorocarbonyl compounds and nitriles or between N-acylimidoyl chlorides and alkynes. Stannic chloride is an effective catalyst for both reactions (c/. Scheme 62). 1,3-Thiazinium perchlorates are synthesized by reacting oxazinium salts with hydrogen sulfide in absolute acetonitrile and then treating the product amides (185) with perchloric acid (Scheme 69) (72S333). 

Thus, thieno[c]tropylium salts (like 228a) are hydrolyzed even by 40% perchloric acid, and are rapidly decolorized by water, alcohols, amines, amides, and carbonyl compounds. The corresponding pyrroles (like 228b) are more stable and are inert toward those reagents (68ZOR907). 

Amino-l,2-dithiolium salts are obtained from either / -oxocarbox-amides or ) -oxocarbonitriles by reaction with phosphorus penta-sulfide, followed by addition of perchloric acid (Scheme 6). These cations, which may also be considered as iminium salts, are deprotonated to the corresponding l,2-dithiol-3-imine by ammonia. ... 

Protonation of ketene 0,N-acetals with strong acids gives rise to the formation of iminium compounds, e.g. (98 equation 57). Ketene OA -acetals are transformed by alkyl halides or acyl halides to a-sub-stituted amides via unstable iminium salts (99 equation 58).Iminium compounds of this type are isol-able if they are immediately precipitated, e.g. as perchlorate salts (100 equation 59), Heterocumulenes such as isocyanates, isothiocyanates or S02 form 1,4-dipoles with ketene OA -acetals, which can be stabilized by protonation with perchloric acid to give salts, e.g. (101 equation 60). 

Color reactions Boric acid (hydroxyquinones). Dimethylaminobenzaldehyde (pyrroles). Ferric chloride (enols, phenols). Haloform test. Phenylhydrazine (Porter-Silber reaction). Sulfoacetic acid (Liebermann-Burchard test). Tetranitromethane (unsaturation). Condensation catalysts /3-Alanine. Ammonium acetate (formate). Ammonium nitrate. Benzyltrimethylammonium chloride. Boric acid. Boron trilluoride. Calcium hydride. Cesium fluoride. Glycine. Ion-exchange resins. Lead oxide. Lithium amide. Mercuric cyanide. 3-Methyl-l-ethyl-2-phosphoiene-l-oxlde. 3-Methyl-1-phenyi-3-phoipholene-1-oxide. Oxalic acid. Perchloric acid. Piperidine. Potaiaium r-butoxIde. Potassium fluoride. Potassium... 

Superacids are, according to R. J. Gillespie [Accounts Chem. Res. 1, 202 (1968)] more acidic than 100 percent sulfuric acid, the most frequently used strong acid solvent. The name superacid was first suggested by Conant in 1927 [Hall, N. F., Conant, J. B. J. Amer. Chem. Soc. 49, 3047 (1927)1 for nonaqueous strong acid solutions (like perchloric acid) or weak bases (like amides) where salt formation is exceptionally complete... 

The oxidation of N-monosubstituted 3-amino-2-aryl-thioacrylic acid-morpholides 20 using hydrogen peroxide in perchloric acid gave 5-morpholino-isothiazolium perchlorates2 21a,c-g (83JPR689) in good yields (Scheme 4). The electrochemical oxidation of 3-amino-thioacryl acid-amides 20 (R = CH2C02Me) is a useful... 

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