Reagents for carbonyl compounds

Carey and Persinger [128] described the derivatization of a number of simple aliphatic carbonyl compounds such as formaldehyde and acetaldehyde with 2,4-DNPH. The derivatives were analyzed on a Corasil II column and monitored at 254 nm. Two HPLC systems were reported for separating the 2,4-DNPH derivatives of thirteen carbonyl compounds ranging from acetaldehyde and acetone to benzaldehyde and salicylaldehyde [136]. One system used a column packed with 1% tris-(2- 

Steroidal ketones have been separated as their 2,4-DNPH derivatives [138, 1391. The neutral I7-keto steroids are of clinical interest in certain disease states the urinary 17-keto steroid level in women is indicative of adrenal activity, and that in men is a composite measure of adrenal and testicular function. Samples of urine and blood hydrolysates can be derivatized with 2,4-DNPH and analyzed by HPLC. In the work of Fitzpatrick et al. 

Honda et al. [142] reported that l-phenyl-3-methyl-5-pyrazolone reacted with reducing carbohydrates aintost quantitatively to yield strongly UV-absorbing derivatives. This reaction differs from other derivatization reactions via the hydroxy group of carbohydrates, such as benzoylation or, p-bromobenzoylation, in that it gives no stereoisomers. This method is especially useful for the analysis of component monosaccharides of gly- 

Glycoproteins were hydrolysed with 2 M trifluoro-acetic acid for 6 h in bioling water bath to yield aldoses, or with 4M HCl for amino sugars. To a sample of aldoses or reducing oligosaccharides (10-500 pmol each) were added a 0.5 M methanolic solution (50 fi ) of PMP and 0.3 M sodium hydroxide (50/il). The mixture was kept for 30 min at 70 °C. After cooling and neutralization, the solution was evaporated to dryness, and the derivatives were extracted into aqueous solution with water/chloroform. 

The separation and retention behaviour of these derivatives was investigated by using various stationary phases and solvents. For the best separation of selected monosaccharides, a Capcell-Pak Cig column and a mixture of 0.1 M phosphate buffer (pH 5) and acetonitrile (4 1 v/v) were the best choice. The use of 18% acetonitrile in 0.1 M phosphate buffer (pH 7.0) shortened the analysis time but gave slightly poorer resolution. Detection was at 245 nm, the absorption maximum, with a detection limit of 1 pmol. This procedure provided gO(jd reproducibility with a relative standard deviation of less than 2.3%. 

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A combination of iodomethyltrimethylsilane and Sm(OTf)2 also works as a methylenating reagent for carbonyl compounds (Scheme 2.28). When this reagent is applied to the reaction with ketones and aldehydes in THF/HMPA at room temperature, the carbonyl compounds are smoothly methylenated this process is known as the samarium-Peterson reaction [69]. 

Derivatisation reagent for carbonyl compounds. Plates (pet. ether). Mp 77-78°. Dec. at 180°. 

Both aldehydes and ketones contain the carbonyl group, hence a general test for carbonyl compounds will Immediately characterise both classes of compounds. The preferred reagent is 2 4-dinilrophenylhydrazine, which gives sparingly soluble phenylhydrazones with carbonyl compounds ... 

There is another possible mechanism for addition of organometallic reagents to carbonyl compounds. This involves a discrete electron-transfer step. °... 

For a detailed transition state analysis of the reactions of allylorganometallic reagents and carbonyl compounds ... 

Davies, S. G. et al., J. Organomet. Chem., 1990, 386(2), 195 This compound is air sensitive and decomposes explosively. Use of the more stable tetrabutylammonium salt as a reagent for carbonylation of alkyl halides is recommended. 

Oximes have been used as protecting groups for carbonyl compounds owing to their hydrolytic stability. Consequently, the development of newer deoximation reagents... 

Sodium cyanoborohydride [123], sodium triacetoxyborohydride [124] or NaBH4 coupled with sulfuric acid [125] are common agents used for the reductive amination of carbonyl compounds. These reagents either generate waste or involve the use of corrosive acids. The environmentally friendlier procedures developed by Varma and coworkers have been extended to a solvent-free reductive amination protocol for carbonyl compounds using moist montmorillonite K 10 day supported sodium borohydride that is facilitated by microwave irradiation (Scheme 6.39) [126]. 

The reactions of allylmetal reagents with carbonyl compounds and imines have been extensively investigated during the last two decades [1], These carbon—carbon bondforming reactions possess an important potential for controlling the stereochemistry in acyclic systems. Allylmetal reagents react with aldehydes and ketones to afford homo-allylic alcohols (Scheme 13.1), which are valuable synthetic intermediates. In particular, the reaction offers a complementary approach to the stereocontrolled aldol process, since the newly formed alkenes may be readily transformed into aldehydes and the operation repeated. 

The addition of allylic boron reagents to carbonyl compounds first leads to homoallylic alcohol derivatives 36 or 37 that contain a covalent B-O bond (Eqs. 46 and 47). These adducts must be cleaved at the end of the reaction to isolate the free alcohol product from the reaction mixture. To cleave the covalent B-0 bond in these intermediates, a hydrolytic or oxidative work-up is required. For additions of allylic boranes, an oxidative work-up of the borinic ester intermediate 36 (R = alkyl) with basic hydrogen peroxide is preferred. For additions of allylic boronate derivatives, a simpler hydrolysis (acidic or basic) or triethanolamine exchange is generally performed as a means to cleave the borate intermediate 37 (Y = O-alkyl). The facility with which the borate ester is hydrolyzed depends primarily on the size of the substituents, but this operation is usually straightforward. For sensitive carbonyl substrates, the choice of allylic derivative, borane or boronate, may thus be dictated by the particular work-up conditions required. 

Enolization is an acid-base reaction (2-24) in which a proton is transferred from the a carbon to the Grignard reagent. The carbonyl compound is converted to its enolate ion form, which, on hydrolysis, gives the original ketone or aldehyde. Enolization is important not only for hindered ketones but also for those that have a relatively high percentage of enol form, e.g., p-keto esters, etc. In reduction, the carbonyl compound is reduced to an alcohol (6-25)... 

Reduction of aldehydes and ketones.4 In the presence of hydrogen chloride (or a Lewis acid), the reagent reduces carbonyl compounds to alcohols in high yield and with high stereoselectivity. However, the reduction of hindered ketones requires a strong Lewis acid (A1C13). Aldehydes are reduced so much more readily than ketones that selective reductions are possible. The reagent is also useful for reduction of a,/5-cnals to allylic alcohols. 

Many of the common laboratory methods for the preparation of alcohols have been discussed in previous chapters or will be considered later thus to avoid undue repetition we shall not consider them in detail at this time. Included among these methods are hydration (Section 10-3E) and hydroboration (Section 11-6D), addition of hypohalous acids to alkenes (Section 10-4B), SN1 and Sn2 hydrolysis of alkyl halides (Sections 8-4 to 8-7) and of allylic and benzylic halides (Sections 14-3B and 14-3C), addition of Grignard reagents to carbonyl compounds (Section 14-12), and the reduction of carbonyl compounds (Sections 16-4E and 16-5). These methods are summarized in Table 15-2. 

It is now generally admitted that this reaction involves both one-electron and two-electron transfer reactions. Carbonyl compounds are directly produced from the two-electron oxidation of alcohols by both Crvl- and Crv-oxo species, respectively transformed into CrIV and Crm species. Chromium(IV) species generate radicals by one-electron oxidation of alcohols and are responsible for the formation of cleavage by-products, e.g. benzyl alcohol and benzaldehyde from the oxidation of 1,2-diphenyl ethanol.294,295 The key step for carbonyl compound formation is the decomposition of the chromate ester resulting from the reaction of the alcohol with the Crvl-oxo reagent (equation 97).296... 

The distillate may contain volatile neutral compounds as well as volatile acids and phenols. Add a slight excess of 10-20 per cent sodium hydroxide solution to this distillate and distil until it is judged that all volatile organic compounds have passed over into the distillate. If necessary, the determination of the refractive index of the distillate or the application of specific chemical tests (e.g. for carbonyl compounds use the 2,4-dinitrophenylhydrazine reagent) should be used to confirm completion of distillation. Keep this distillate (S,) for Step 4. 

This compound is air sensitive and decomposes explosively. Use of the more stable tetrabutylammonium salt as a reagent for carbonylation of alkyl halides is recommended. 

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