Carboxylic acid hydroxyl peaks

FIGURE 5.9 Carboxylic acid hydroxyl peaks. Arrows near 1890 and 2130/2160 point out combination bands relating to the nonbonded hydroxyl. (From Weyer, L.G. and Lo, S.-C., in Handbook of Vibrational Spectroscopy, Chahners, J.C. and Griffiths, P.R., John Wiley Sons, 2002. With permission.)... 

Characteristic markers of Venice turpentine are larixol and larixyl acetate, but in many cases they may remain undetected, as larixyl acetate hydrolyses and the methylation of hydroxyl groups is not as effective as for carboxylic acids. On-line derivatization with tetramethylammonium hydroxide (TMAH) is, for instance, scarcely effective on hydroxyl groups and involves a number of secondary reactions (isomerization, dehydration and cleavage of hydrolysable bonds) due to the strong alkalinity of the TMAH solution. When the experimental conditions are such that THM of labdanes occurs larixol and larixyl acetate are detected as a single peak since in the derivatization process larixyl acetate is hydrolysed to larixol [29]. 

Compounds containing a hydroxyl group (OH) have a strong very broad absorption in the 3,600-2,500 cm region of the spectrum. The most common examples are the alcohols and the carboxylic acids. The combination of a broad 3,600-2,500 cm band with a 1,700 cm peak often indicates a carboxylic acid (or amide — keep reading). 

Another series of antiinflammatory carboxylic acids that are derived from cortienic acid (107), a minor adrenal metabolite, has been described (104,105). Esterification of both the 17a-hydroxyl group and the carboxylic acid of (107) were required to develop a compound of high topical potency with low systemic activity. Peak activity was generally associated with a 17a-propionoxy group and a 17P-fluoromethoxy carbonyl (eg, (108)), or 17 (3 - me tho xyc arb o nyl residue. 

The distinctive peak at 12 S serves to identify the carboxylic acid. For the hydroxyketone, the absorption of the hydrogen on the oxygen-bearing carbon (3.5-4.5 S) is significant. The position of absorption of the hydroxyl hydrogen is unpredictable, but addition of D2O to the sample can be used to identify this peak. 

Flood gun conditions, 0.3 ma, 5 eV. The C-Is alkyl line was approximately 279.0 eV the spectra above are charge-referenced to 284.0 eV for the alkyl carbon line. Spectrum A is the as-received material note the presence of the aromatic satellite at 6.7 eV from the main carbon line at 284.0. Note also the absence of any carbon-oxygen functionalities as evidenced by the lack of structure between 284 and 290 (a) as-received material (b) methanol-cleaned (c) oxygen plasma-treated material. Note the decrease in the satellite line at 297 eV it has disappeared to nearly background level. Also note the presence now of two carbon-oxygen functionalities as evidenced by apparent peaks at about 288.6 and 286.4 eV, characteristic of ester or carboxylic acid, and ether or hydroxyl carbon, respectively. 

Sample Carboxylic acid (meq/g) Ester, amide, lactone (meq/g) Percentage contribution of ester, amide, lactone to carbonyl peak (%) Ketone (meq/g) Phenolic hydroxyl (meq/g)... 

Infrared The most characteristic peaks in the infrared spectra of carboxylic acids are those of the hydroxyl and carbonyl gronps. As shown in the infrared spectrum of... 

The confirmation of the oxidation of the primary hydroxyl group located at C to a carboxylic acid group is based on the two peaks (at 62 and 63 ppm) in the (CH2OH) region and on the peak at 183 ppm in the carbonyl region of the spectrum. This is in accordance with the interpretation of Eyde et al.72... 

Total extracts and/or liquid chromatographic subfractions are then analyzed by capillary colnmn gas chromatography nsing a flame ionization detector. Except for hydrocarbon fractions, derivatization is commonly applied to render polar lipids more volatile in order to reduce gas chromatographic retention times and to improve peak shape at the detector. Carboxylic acids are usually transformed into their methyl esters, and hydroxyl or amine gronps into their trimethylsilyl ether derivatives. Alternatively, both acid and hydroxyl groups can be silylated. Acetate formation is another common derivatization method. A variety of derivatization reagents are conunercially available for this purpose. 

Ketoprofen is rapidly and nearly completely absorbed on oral administration, reaching peak plasma levels within 0.5 to 2 hours. It is highly plasma protein bound (99%) despite a lower acidity (pKa = 5.9) than some other NSAIDs. Wide variation in plasma half-lives has been reported. It is metabolized by glucuronidation of the carboxylic acid, CYP3A4 and CYP2C9 hydroxylation of the benzoyl ring, and reduction of the keto function. 

Figure 3.45 shows the NMR spectra for an amide, a class of compounds with — NH2 substituted for the hydroxyl group of a carboxylic acid. The compound here is propiona-mide, CH3CH2CONH2. There are three unique carbon atoms, the carbonyl carbon in the amide and two alkyl carbons. From Fig. 3.39, the carbonyl carbon in an amide is expected to absorb in the 165-175 ppm range the peak occurs at 177 ppm in this spectrum. The methyl carbon is located at 10 ppm, while the methylene carbon appears at 29 ppm. The proton spectrum was discussed earlier, but it is worth noting again the two small broad peaks due to the nonequivalent amide protons at 6.3 and 6.6 ppm. 

---