Ultraviolet absorption ketones

The lack of strong ultraviolet absorption by oxiranes is particularly useful for monitoring the epoxidation of a, -unsaturated ketones. 

The first, and to this writing still only case of a ketone a-cleavage-recombi-nation sequence in the steroid field was reported by Butenandt, who found that 17-ketones epimerize at C-13. Ultraviolet irradiation of either stereoisomer produces an equilibrium mixture in which the thermodynamically more favored 13a-compound cf. (15)] with cw-fusion of rings C and D predominates at room temperature. As ultraviolet absorption energies and intensities of the two isomeric ketones are practically identical, the equilibrium composition depends largely on the rate of the competing recombination process from (14). For further examples of the photoisomerization at C-13 of 17-ketosteroids, see ref. 8, 12, 15 and 43. 

The oil thus obtained was dissolved in 4O0 cc of methanol and refluxed during one hour with 150 cc of 4N hydrochloric acid. The mixture was poured into a sodium chloride solution and extracted with ethyl acetate, washed to neutral, dried and evaporated to dryness. The product was a yellow oil which showed an ultraviolet absorption maximum characteristic of a A -3-ketone. 

The ultraviolet absorption spectra of ketones are characterized by a low intensity n -n absorption band in the 270-300 nm region, and a high intensity... 

Wavelengths tor Maximum Ultraviolet Absorption of Some Carboxylic Acids, Aldehydes, and Ketones (n--- n )... 

It may be of interest to compare the photochemistry of the unsubstituted cyclic ketones. The effect of ring size on the ultraviolet absorption spectrum has been discussed (4,22) although its pertinence to the photochemistry is not obvious. 

The photochemical reactions of three a/3-unsaturated cyclic ketones have been reported. In these cases, it appears that the reaction is that of the olefinic group although the wavelength of the incident radiation is at the ultraviolet absorption of the carbonyl group. Photolysis of 2-cyclo-pentenone (16), carvone (XXXV) (7,12) and y-tropolone methyl ether... 

Methylsinomeninic acid [xci, R = H] and 1-bromomethylsinome-ninic acid [xci, R = Br] are formed when methylsinomeninone [73] and 1-bromomethylsinomeninone [44] respectively are oxidized with hydrogen peroxide. Similarly the oxidation of 1-bromosinomeneine ketone [lxxvi] affords 1-bromosinomeneinic acid [xcii] [73]. The ultraviolet absorption spectra of [xc, R = H], [xc, R = Br], and [xci, R = H] are very similar to that of sinomenine hydrate, which in turn is almost identical with that of sinomenine [73]. 

Polypropylene usually exhibits an ultraviolet absorption extending beyond 290 nm, although the pure polymer is not expected to show an absorption beyond 200 nm. Photodegradation of polypropylene is thus likely to be initiated by impurities such as hydroperoxides or ketonic oxidation products formed during the processing of the sample. Such behaviour is similar to that already discussed for polyethylene. 

Base-catalyzed reactions of amino sugars with 2,4-pentanedione in a nonaqueous solvent (piperidine-triethylamine-methanol) have also been reported. The products obtained under these conditions from 2-amino-2-deoxy-D-glucose are 3-acetyl-2-methyl-5-(D-ami)OTo-tetrahydroxybutyl)-pyrrole (2) (in about 90% yield) and 2-deoxy-2-n(4-oxopent-2-enyl)-amino]-D-glucose (28). Proofs that structure (28) is correct were (a) the ultraviolet absorption, typical of a -amino a,j3-unsaturated ketone, (b) a positive test with the ferric chloride reagent, and (c) quantitative... 

Hydroxyketone may undergo either dehydration (Reaction 9) or photolysis (Reactions 10 and 11). Dehydration yields carbonyl groups with conjugated ethylenic unsaturation, which has characteristic ultraviolet absorptions depending on the number of double bonds (23). Table IV shows the ketone distribution and total number of statistical... 

Whilst on oxidation of oxoisoatisine (III) the ethylenic linkage in the allyl position to the secondary hydroxyl group is attacked, such reaction is not possible with dihydrooxoisoatisine (IV) instead, the primary hydroxyl group suffers initial oxidation (though slowly) and a monocarboxylic acid (X) results which may be further oxidized to a ketocarboxylic acid (XI), the ketonic group of which is readily detected by its ultraviolet absorption. 

The formulation of aconitoline as an a , 3-unsaturated ketone should be capable of direct proof, since such ketones and their derivatives generally have characteristic ultraviolet absorption spectra unfortunately, the absorption spectrum of aconitoline is not on record, and such direct evidence in support of the reaction scheme outlined (51) is therefore not yet available. It is clear, however, that the oxidation according to the above scheme cannot proceed unless the hydroxyl group in the /3-position to the methoxyl is free some indirect evidence may be adduced for the reaction scheme since triacetylaconitine (53) in which this group is esterified is not attacked whilst mesaconitine (51) is. Moreover, of the two alkaloids, hypaconitine and pseudaconitine, containing one hydroxyl group less than aconitine, the latter (54) is, but hypaconitine (51) is not, oxidized by chromic acid it appears, therefore, that the hydroxyl group which hypaconitine lacks is that in the 3-position to one of the methoxyls, that specifically attacked by chromic acid. 

Oxidation may then be assumed (71) to give the keto acid, in which the ethylenic linkage is conjugated with the carbonyl group this placing of the ethylenic linkage is purely speculative and not fully corroborated by the ultraviolet absorption spectrum (which, instead of the high-intensity maximum near 2350 a. expected for an isocyclic a,/3-unsaturated ketone. 

As mentioned earlier, one of the structural characteristics shared by the six active adrenal steroids is the a,/3 unsaturated ketone at position 3. As a result, these compounds absorb ultraviolet light at wave lengths which vary slightly from 238 to 242 m/i. Even though a comparison of the ultraviolet absorption spectra does not usually allow unequivocal differentiation among the six steroids, it serves as a very useful quantitative technique (see Table II) for the determination of concentrations of these compounds in mixtures with other materials having dissimilar absorption characteristics. 

The non-ketonic oestrogens are more important pharmaceutically the parent materials are usually not assayed as such, but are controlled by measurement of physical characteristics such as optical rotation or ultraviolet absorption (see Table 29). Where they appear in formulations (frequently as oily injections) the reaction most commonly employed for their determination is that due to Kober in which a magenta colour is formed by reaction of the oestrogen with phenolsulphonic acid and sulphuric acid the colour produced has an absorption maximum at about 525 m/Uy but other oestrogens also react to give a brownish colour with absorption maximum at 420 m. The method is further complicated by the fact that... 

FIGURE 48.12 Ultraviolet absorption spectra of ketone 70 and its solid state photoproduct 94 illustrating the wavelength selected for excitation in the solid state (X. > 350 run). Irradiation at this wavelength allows for deeper penetration in the crystal and reduces local heating from excess photon energy. 

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