Benzyl alcohol absorption

Hydrogenolysis of aromatic carbonyls occurs mainly by conversion to the benzyl alcohol and its subsequent loss. If hydrogenolysis is desired, the usual catalyst is palladium 38). Hydrogenolysis is facilitated by polar solvent and by acid (55). For instance, hydrogenation of 3,3-dicarbethoxy-5,8-dimethoxy-l-tetralone (5) over 5% Pd-on-C gave 6 quantitatively 54) when hydrogen absorption ceased spontaneously. 

An unusual by-product was obtained in small yield in palladium-catalyzed reduction of 2-amino-4,5-dimethoxyindanone hydrochloride, The reduction was done in two stages first, a rapid absorption of 1 mol of hydrogen at 38 C to give the amino alcohol, and then a much slower reduction in the presence of HCIO4 at 70 "C. The rearranged by-product was shown to arise from attack of acid on the amino alcohol (50), Resistance to hydrogenolysis is characteristic of / -amino aromatic alcohols (56), a fact that makes reduction of aromatic oximino ketones to amino benzyl alcohols a useful synthetic reaction. 

Wan also studied hydroxybenzyl alcohols based on the naphthalene chromo-phore.40 Naphthols 50 and 51 were both examined for their ability to photogenerate naphthoquinone methides 52 and 53, respectively (Eqs. 1.12 and 1.13). While 50 underwent very efficient photosolvolysis, presumably via naphthoquinone methide 52, 51 was essentially unreactive when exposed to light. The inability of 51 to photogenerate 53 is a rare example where the generality of the photodehydration of benzyl alcohols fails. LFP of 50 yielded a very strong visible absorption (A x = 410 and 700 nm) that decayed in aqueous acetonitrile with a lifetime of 34 ps (Fig. 1.2). This transient was assigned to naphthoquinone methide 52 due in part to its efficient quenching when the nucleophilic ethanolamine was added. 

Recently, the electrochemical behavior saturated alcohols, that is, propargyl alcohol (HCSCCH2OH, PA) [145], benzyl alcohol (C6H5CH2OH, BA) [146] andallylalcohol [147], has been studied at Pd electrodes in an acid medium by cyclic voltammetry, chronoamperometry, and on-line mass spectrometry. For BA, it was observed that the fragmentation of the molecules occurs at potentials in the hydrogen ad-sorption/absorption region of palladium, whereas for PA the adsorbates maintain the C3-chain. On the other hand, the yields of the electroreduction and electrooxidation products for both PA and BA differ from those obtained at Pt [146,148,149]. 

Benzaldehyde. The addition of less than stoichiometric quantities of benz-aldehyde to CoH (H2 atmosphere) did not result in hydrogen absorption. However, when this procedure was carried out with CoH containing added alkali (KOH, 2x cobalt concentration), hydrogen was taken up, 1.0 atom of hydrogen being absorbed per mole of substrate. Since benzyl alcohol was isolated in 66% yield, it is assumed that a portion of the product may have been formed via a competitive Cannizzaro reaction. Reinforcing this assumption is the observation of an apparent depletion of alkali during the run. 

Besides local toxicity, discussed above, there are numerous other modes of potential adverse interactions involving excipients (19,20). Many of these pose little threat provided the amounts of excipients are constrained to certain levels. Excessive amounts, however, can cause problems, particularly for patients who are intolerant of even modest levels. Commonly used phosphate buffers may cause calcium loss with formation of insoluble calcium phosphates when such buffers are administered in over-ambitious amounts (21). Calcium phosphate precipitation has been noted particularly in nutritional parenteral admixtures for neonates because of the high nutrient requirements. Similarly, renal toxicity has been associated with depletion of zinc and other trace metals caused by large parenteral doses of ethylenediaminete-traacetic acid (EDTA) (22). Excessive absorption of glycine solutions, when used as irrigants during transurethral resections, can cause hyponatremia, hypertension, and confusion (23). The use of preservatives has been associated with cardiac effects in a few patients (24). Premature neonates were found to be at risk for receiving toxic amounts of benzoic acid or benzyl alcohol in bacteriostatic solutions used to flush intravenous catheters (25). 

Benzyl alcohol [100-51-6] M 107.2, f.p. -15.3°, b 205.5 , 93°/10mm, d 0.981, n 1.54033. Usually purified by careful fractional distn at reduced pressure in the absence of air. Benzaldehyde, if present, can be detected by UV absorption at 283nm. Also purified by shaking with aq KOH and extracting with peroxide-free ethyl ether. After washing with water, the extract was treated with satd NaHS sol, filtered, washed and dried with CaO and distd under reduced pressure [Mathews JACS 48 562 7926]. Peroxy compounds can be removed by shaking with a soln of Fe(II) followed by washing the alcohol layer with distd water and fractionally distd. 

Benzyl acetate is quite soluble in lipids and therefore readily absorbed from the gastrointestinal tract and lung, as well as through the skin, in the species investigated. The absorption after oral administration in the rat was delayed if it was administered in com oil or propylene glycol as compared to neat [wet/zy/ene- Cjbenzyl acetate (Chidgey Caldwell, 1986) the peak plasma concentration of benzyl acetate-derived radioactivity occurred later after 1 h versus 4-6 h) and was lower at a 500 mg/kg benzyl acetate dose at 5 mg/kg benzyl acetate, there was no difference. The urinary excretion of the metabolites was also delayed by com oil, but the extent of absorption seemed not to be affected more than 80% was absorbed and excreted within 24 h, mainly in urine and, ultimately, less than 5% in faeces. In plasma and urine, no intact benzyl acetate was detected at any time only its metabolites were present (Chidgey Caldwell, 1986). Benzyl acetate is rapidly hydrolysed by esterases to benzyl alcohol and acetate (Yuan et al., 1995). These esterases are present in plasma and probably also in the tissues it is... 

Intramolecular protonation on the more hindered face of a steroid from a neighbouring hydroxyl group best explains a reversal of diastereoselectivity in the Birch reduction of styrene double bonds.266 The kinetics and product distribution of lithium metal reduction of benzaldehyde to benzyl alcohol in THF have been studied electron transfer from Li to PhCHO occurs in a slow step, but absorption of the PhCHO onto the metal surface is also crucial in determining the overall kinetics. The proposed mechanism successfully accounts for the formation of minor products, benzoin and... 

The aromatic carbons in the 13C spectrum of benzyl alcohol (C6H5-CH2-OH Fig. 3.53) result in a similar absorption pattern to that of toluene. The aliphatic carbon appears at 8 64.3, a downfield shift of more than 40 p.p.m. as a result of the replacement of one of the hydrogens of the methyl group by a hydroxyl group. The six carbons of the aromatic ring give a group of four absorptions between S 126.9 and <5 140.9. 

The aromatic carbon atoms in phenylacetic acid (C6H5-CH2-C02H Fig. 3.55) result in a similar absorption pattern to that described above for benzyl alcohol. The methylene carbon appears at <541.1 compared with <564.2 in benzyl alcohol. It is instructive to compare the chemical shift of the carbonyl carbon in phenylacetic acid (<5178.3), crotonaldehyde (<5 192.2) (Fig. 3.52) and 4-methyl-... 

The broad, intense absorption at 3300 cm-1 is attributable to a hydroxyl group. Although both phenol and benzyl alcohol are possibilities, the peaks at 2800-2900 cm-1 reveal the presence of hydrogen bonded to -hybridized carbon. All carbons are sp2-hybridized in phenol. The infrared spectrum is that of benzyl alcohol. 

There may be times when an orthogonal basis may not span the space of a mixture spectrum. For example, suppose a mixture was contaminated with a substance like benzyl alcohol that has a UV/visible spectrum different from acetophenone and benzophenone. In this case, the absorption signal due to all three components will not be modeled by the two eigenvectors from the factor analysis of acetophenone and benzophenone mixtures. 

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