Carbonyl derivatives hydrochloride

Carbonyl derivatives can be determined quantitatively through the notion of the hydroxylamine index, whose final operation is an acid-base titration. Hydroxylamine hydrochloride reacts with the carbonyl function in judicious conditions according to the scheme ... 

A comparison of the relative basicities of pyrrole, furan and thiophene may be made by comparing the pK values of their 2,5-di-t-butyl derivatives, which were found to be -1.01, —10.01 and —10.16, respectively. In each case protonation was shown by NMR to occur at position 2. The base-strengthening effect of alkyl substitution is clearly apparent by comparison of pyrrole and its alkyl derivatives, e.g. A-methylpyrrole has a pKa. for a-protonation of -2.9 and 2,3,4,5-tetramethylpyrrole has a pK of 4-3.7. In general, protonation of a-alkylpyrroles occurs at the a -position whereas /3-alkylpyrroles are protonated at the adjacent a-position. As expected, electron-withdrawing groups are base-weakening thus A-phenylpyrrole is reported to have a p/sTa of -5.8. The IR spectrum of the hydrochloride of 2-formylpyrrole indicates that protonation occurs mainly at the carbonyl oxygen atom and only to a limited extent at C-5. 

The Apomorphine-derived alkaloid PO-3 (129) was isolated as violet needles after crystallization from acetone and ether from Papaver orientale (66MI2), but was not found in the green solutions of autoxidized apomorhine hydrochloride (62M941, 68HCA683) (Scheme 51). No anion was detected by elemental analysis. The pA"a of PO-3 is 3.88 0.02 in 50% ethanol. The IR spectrum displays no carbonyl absorption between 1650 and 1700 cm (69MI2). The UV absorption maxima of PO-3 are in agreement with the formulation of a mesomeric betaine [T-max (EtOH) = 310... 

Penicilloic acid 5, the substrate for the projected lactamization reaction, could be derived from the suitably protected intermediate 6. Retrosynthetic disassembly of 6, in the manner illustrated, provides D-penicillamine hydrochloride (7) and tert-butyl phthalimido-malonaldehydate (8) as potential building blocks. In the synthetic direction, it is conceivable that the thiol and amino groupings in 7 could be induced to converge upon the electrophilic aldehyde carbonyl in 8 to give thiazolidine 6 after loss of a molecule of water. 

Free formaldehyde is reacted with acetylacetone in the presence of an excess of an ammonium salt to form the yellow fluorescent compound, 3,5-diacetyl-1,4-dihydrolutidine and subsequently determined spectrophotometrically in methods A-E (14). In these methods, the test sample must be colorless and free from other carbonyl compounds. Some other derivatives have been used to analyze formaldehyde. For example, formaldehyde was reacted with sodium 4,5-dihydroxy-2,7-naphthalene disulfonate in sulfuric acid solution to yield a purple color (580 nm) and then subjected to colorimetric analysis. A purple-colored pararosaniline derivative was used to analyze formaldehyde in air (15). Air sample was passed through an aqueous solution which contained 0.4% of 3-methyl-2-benzothiazolone hydrazone hydrochloride and then a dye produced was determined at 635 or 670 nm (16). Molecular sieve (1.6 mm pettet) was used to trap formaldehyde in air samples. The formaldehyde... 

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