Benzophenone in ethers

There is still considerable interest in the products of irradiation of hydrogen abstracting ketones for example, Plank96 has reported that benzophenone in ether gives benzophenone pinacol in higher yield when naphthalene is added. It was suggested that the pinacol is formed from some intermediate which is photochemically destroyed in the absence of a quencher. Challand97 has isolated products from addition of ether to acetophenone. 

The best known hydrogen abstraction reaction of aromatic carbonyl compounds is that involved in the formation Of benzopinacol on ultraviolet irradiation of solutions of benzophenone in ethers and alcohols. 

A Hammett treatment of the retiction ot ethyl-magnesium bromide with benzophenone in ether [109] show ed a linear plot for the ratio iddi-tion/reduction with a p = 1. Changing from DEE to THE led to two linear plots intersecting at (7 = —0.15. The change in p must be interpreted as a chance in mechanism for the addition. The... 

The kinetics of the reaction between methylmagnesium bromide and benzophenone in ether/benzene has been explored (77) and a rate process consistent within runs with the kinetic expression, rate = [RMgX] [ketone] reported. Unfortunately over the short concentration spans employed "between runs the k s are inversely proportional to Grignard concentration. In THF the same reaction is second order within a run, if only initial points are considered, the second half of the R groups being utilized very slowly (61). In the ether/benzene system Me2Mg reacts with benzophenone by a process claimed to be third order, but the intended mechanism is not clear, nor do the data support the third-order expression. Initial rates in THF are claimed to be second order (61). 

A soln. of benzophenone in ether or benzene added dropwise at —30° to ethyl-magnesium bromide and anhydrous cobaltous chloride in ether, and the product isolated after 2-3 hrs. benzopinacol. Y 98%.—High yields are obtained only at low temp. F. e. s. R. Pallaud and J.-F. Treps, G. r. 260, 1187 (1965). 

Ether was distilled from sodium ketyl of benzophenone. The dissolution of n-butyllithium in ether was slightly exothermic. 

The rates of the reactions of several aromatic ketones with alkyllithium reagents have been examined. The reaction of 2,4-dimethyl-4 -(methylthio)benzophenone with methyl-lithium in ether exhibits the rate expression ... 

A) 1-(2-Amino-5-chlorophenyll-1-(2-fluorophenyll-2-a2a-but-1-en-4-ol A mixture of 40 g of 2-methylimidazole hydrochloride and of 90 g of 2-amino-5-chloro-2 -fluoro-benzophenone in 240 ml of ethanolamine is heated at 135 for 2 hours. After cooling, the reaction mixture is poured into an aqueous sodium bicarbonate solution. The mixture is extracted with ether, the organic phase is washed repeatedly with water and is dried over sodium sulfate, and the solvent is evaporated to dryness. The residual oil is chromatographed on a silica column, elution being carried out with a 50/50 mixture of cyclohexane and ethyl acetate. 

Sodium methoxide (1.2 g) in dimethylformamide (150 ml) was stirred with 3,5-dim ethoxy-4 reaction mixture was then treated with /3-morpholinoethyl chloride (3.4 g) and heated for 1 hour at 140°C, then evaporated to dryness, and treated with water to give a solid material. The mixture was filtered, washed and crystallized from cyclohexane to give 3,5-di-methoxv-4 -chloro-4-( morpholinoethoxy)-benzophenone (6.5 g), MP 91°C to 92°C. The product was then reacted at about 0°C with gaseous hydrogen chloride in ether to give, after crystallization from isopropanol, the corresponding hydrochloride which hada MPof 187.9°C. 

Another photocyclization to a benzo[c]phenanthridine was reported (127). Oppenauer oxidation of ( )-ophiocarpine (92) with potassium fm-butoxide and benzophenone in dioxane effected C-6—N bond cleavage to afford the hydroxyisoquinoline 219 via berberinephenolbetaine (121) (Scheme 39). Although photolysis of 219 gave only the oxepine 221, that of its methyl ether 220 furnished directly norchelerythrine (222) through electrocyclization followed by spontaneous elimination of methanol. 

This reaction is the reverse of the initial ketyl radical formation by the benzophenone triplet and is therm Q4ynamically favorable. The experiments using optically active alcohols as source of hydrogen atoms show, however, that under normal conditions this reaction is unimportant. This is probably due to other, more efficient pathways for reaction of the ketyl radicals or perhaps to diffusion rates which separate the radicals before reverse transfer can occur. That this reaction can be important in some cases even without the presence of sulfur compounds was shown by studying the photoreduction of benzophenone in optically active ethers.<68) Although the reaction of benzophenone in methyl 2-octyl ether is only 0.17 times as fast as that in isopropanol, ethers can be used as sources of hydrogen atoms for photoreduction ... 

A photosensitized dimerization of an isolated olefin, norbomene, has been reported by Scharf and Korte.<3) Irradiation in acetone or in the presence of acetophenone (Et = 74 kcal/mole) produced dimers (5) and (6) as major products. However, benzophenone (Et = 69 kcal/mole) failed to sensitize the reaction to (5) and (6), but in ether solution led to the quantitative formation of benzpinacol and in benzene to the oxetane (7) in 80% yield. Sensitizers of intermediate energy, such as xanthone (Et — 72 kcal/mole), demonstrated a competition between energy transfer to form triplet norbomene and cycloaddition to form the oxetane ... 

The thermal decomposition of />-nitrotriphenylmethyl hydroperoxide in benzene gives -nitrophenol 32%, phenol 9%, >-nitro-triphenylcarbinol 23%, -nitrobenzophenone 14%, and no benzo-phenone the decomposition in ether plus sulfuric acid gives -nitro-benzophenone 94% and phenol 81%.817 The latter reaction is very probably ... 

Ashby and Yu have studied the kinetics of reduction of benzophenone with TIBA in ether and showed that the overall kinetic rate expression is second order, first order in TIBA and first order in ketone (151). The observed activation parameters were AG - 18.8 kcal/mol AH = 15.8 kcal/mol and AS = - 10.1 e.u. The negative entropy of activation is consistent with a cyclic transition state for the rate-determining hydride-transfer step. A Hammett study gave a value of p = 0.362, supporting nucleophilic attack by the aluminum alkyl on the carbonyl group in the rate-determining step. 

The photoreduction of nitrobenzene using p5o ex filtered light from a medium pressure mercury arc was studied in petroleum, toluene, ether, 2-propanol, tert-butyl alcohol, diethylamine, triethylamine, aqueous solutions of 2-propanol and diethylamine and also in aqueous t-butylalcohol containing sodium boro-hydiide 3 >. Varying amounts of aniline, azo- and azoxybenzene were obtained. In the presence of a fourty-fold excess of benzophenone, a six-fold increase in the rate of aniline formation in ethereal solution was observed, and aniline formation was completely suppressed by addition of biacetyl or octafluomaphthalene Since unreacted nitrobenzene could be recovered in these experiments, it is demonstrated that the triplet state of nitrobenzene was quenched. 

For the reactions of MeLi with benzophenone and the benzophenone that was labeled at the carbon atom of the carbonyl group, ratio is 1.000 in ether at 0°C. Under the same conditions, this ratio is 1.023 for MeLi addition to the carbonyl pair of 2,4,6-trimethylbenzophenones... 

Photolysis of diphenyldiazomethane in MeCN solution in the presence of sufficient 84 yields benzophenone in >90% yield and tetramethyipiperidine in equimolar amounts. A similar photolysis with 4-hydroxy-TEMPO (84, X = OH) gives benzophenone and ether (85) in 16 1 ratio, indicating that attack at the nitroxide center predominated even though it is more hindered than the OH group. In the case of cyclohexanol, which is used as a reference substrate for 4-hydroxy-TEMPO, the reaction with DPC gives >90% yield of the expected ether. ... 

C6H5 -NrN-QHs +QH, -NK-NK-QHs dk violet crysts prepd from azobenzol and 4-phenyl benzophenone K salt in ether. It is readily oxidized in air to form azobenzene. This... 

Unless otherwise stated, all operations are carried out in flame-dried glassware under an inert gas atmosphere using standard Schlenk techniques.7 Solvents were dried over sodium (light petroleum, bp 40-60°C) or sodium benzophenone (diethyl ether, THF) or calcium hydride (acetonitrile). Li[BHEt3] in THF (Superhydride ) and sodium bis(trimethylsilyl)amide were used as purchased (Aldrich). 

Semistabilized ylides such as benzylidene- (55) or methylene- (59) triphenylarsorane reacted with carbonyl compounds in ether to give olefins as well as oxiranes. For example, reaction of methylene triphenylarsorane with benzophenone gave, besides triphenylarsine oxide... 

The rate of addition of dimethylmagnesium to excess diphenylmethanone (benzophenone) in diethyl ether initially is cleanly second order, that is, first order in ketone and first order in (CH3)2Mg. As the reaction proceeds, the rate no longer follows a strictly second-order rate overall. Suggest how the apparent specific rate could change as the reaction proceeds. 

Exercise 27-14 Diphenylmethanone (benzophenone) in diethyl ether solution adds an electron from a sodium atom and forms a radical anion ... 

Figure 13.4 (a) Absorption spectra of benzophenone (ethanol, 20°C) and naphthalene (ethanol + methanol, — 180°C). (b) Phosphorescence emission spectra at — 190°C in ether + ethanol, under steady irradiation at 3660 A. Benzophenone, 2 x 10 2 M benzophenone + naphthalene, 2 x 10-2 M and 3.2 x 10-1 M, respectively concentration of pure naphthalene (solid line) not known. From A. Terenin and V. Ermolaev, Trans. Faraday Soc., 52, 1042 (1956). Reproduced by permission of the Faraday Society. 

Reaction of phenylsilene 473 with benzophenone in boiling dioxane gives directly the silyl enol ether 477, the thermal decomposition product of the initially formed oxasilirane E/Z-478 (equation 158)243. 

In contrast to the complicated mechanisms proposed for the addition of trimethylaluminium to benzophenone in solvent benzene, addition in solvent ether is straightforward26. Trimethylaluminium probably exists as the monomeric complex Me3Al-OEt2 in ether, and addition was found to obey the second-order rate equation, dP/df = A 2bs [Me3Al][Ph2CO], where P denotes the product of addition. The mechanism of addition was described26 by the reactions... 

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