Ketones in the solid

A small number of examples is available for the synthesis of E and Z isomers of oximes. In many cases, E isomers were obtained either from the Z forms (by the hydrochloride method) or isolated by column chromatography. Often, the reagents that have been used for oximation of aldehydes and ketones also catalyze the interconversion of Z and E isomers. The rate of equilibration of a mixture of Z and E isomers and the position of the equilibrium is temperature-dependent ". In 2001, Sharghi and Sarvani reported a convenient method for controlling the stereochemistry of the reaction of hydroxylamine hydrochloride with aldehydes or ketones in the solid state. The highly stereoselective conversion of aldehydes and ketones to their corresponding oximes... 

Benzoin, a-furoin, and most probably a-thenoin, however, are oxy-ketones in the solid state and in carbon tetrachloride. This has been... 

Table 15-2. Reduclion of ketones in the solid state by NaBH4 ).

A Grignard reaction also occurred in the solid state, but some reactions gave different results from those observed in solution. In particular, reactions of ketones in the solid state gave more reduction products than addition products [9]. 

Photochemical hydrogen abstraction by ketones in the solid state has drawn much attention (5-11,20-24). As a result of detailed studies on the tetrahydronaphthoquinone system (5,6), the following geometrical requirements for the reaction have been... 

A polymeric pinacol,poly[3-methyl-2-(4-vinylphenyl)-2,3-butanediol],has been prepared by radical polymerization of the styrenic diol monomer and shown to be cleanly and quantitatively converted to a non-conjugated ketone in the solid state by reaction with a photochemically-generated acid [151,348, 350]. The rearrangement reaction can be readily monitored by IR spectroscopy as the disappearance of the hydroxyl OH absorption is accompanied by appearance of a new ketone carbonyl absorption (Fig. 116). Since a polar alcohol (isopropanol) dissolves the polar diol polymer in the unexposed regions but cannot dissolve the less polar ketone polymer produced in the exposed regions, the resist functions as a negative system with alcohol as a developer. The diol polymer is stable thermally to 225 °C in the absence of acid. 

The thermal degradation of poly(vinyl alcohol) was studied, both in the solid and molten state [47]. The thermal degradation of PVOH in the molten state consisted of water elirrtina-tion and chain scission, via a six-member transition state, leading to the formation of volatile products including satrrrated and rrrtsatrrrated aldehydes and ketones. In the solid state, thermal degradation of PVOH was exclusively by elimination of water. 

Boch, R., Bohne, C., and Scaiano, J. C., Time-resolved diffuse reflectance studies of 5-phenyl ketones in the solid state conformational and chiral control of triplet lifetime, /. Org. Chem., 61, 1423, 1996. 

Rao, V. P. and Fech, J., Stereoselective photodimerization of SnCl4 complexes of cycHc a,P-unsat-urated ketones in the solid state, /. Photochem. Photobiol. A Chem., 67, 51-56,1992. 

Alternatively, dissolve approximately equivalent amounts of the aldehyde (or ketone) and the solid reagent in the minimum volume of cold glacial acetic acid, and reflux for 15 minutes. The p-nitrophenyl-hydrazone separates on cooling or upon careful dilution with water. 

The 0,N-dideuterated enol was formed by hydrolysis of the O-trimethylsilyl ether 123 (R = TMS) (in 80% [D6]DMSO/20% D2O with 5. lO " M DCl). N-Methylindoxyl (formed by hydrolysis of its acetate) exists in the solid state as a mixture of the enol and the keto tautomers (34% enol/66% keto). The NMR spectrum of freshly prepared solution in DMSO demonstrated signals of both enol and keto forms. However, at equilibrium (reached in 18 h at RT) the ratio of enol to ketone depends strongly on the polarity of the solvent used thus, in [Dg]DMSO the tautomeric mixture contains 92% enol, while in CDCI3 the keto form predominates (97%). A solution with 100% enol could be generated by hydrolysis of its O-trimethylsilyl ether [conditions 80% [Dfi]DMSO/20% D2O with 5 10" M DCl at 32°C (86TL3275 87PAC1577 88TL250)]. 

This is hardly stable and it was not until suitable conditions of dilution were found that it was possible to handle it in industry. Even at low temperatures it detonates easily, when it is in the solid or liquid state. Detonations occurred during attempts at liquefaction. Ite dilution in nitrogen at -181° stabilises it, but there was an accident under these conditions, which was due to the presence of carborundum that makes it sensitive to impact. In the gaseous state, it detonates at a pressure of 1.4 bar and above. It can only be kept under pressure when it is in a solution of acetone in which it is highly soluble. Alcohols to C4, ketones to C4, diols C3 and C4, and carboxylic acids to C4 all play the same stabilising role as acetone. 

As it pertains to the solid state photodecarbonylation reaction, the model assumes that most aliphatic ketones have similar excitation energies, that reactions are more likely along the longer-lived triplet excited state, and that each reaction step must be thermoneutral or exothermic to be viable in the solid state. " Using acetone and its decarbonylation intermediates as a reference reaction (dashed lines in Fig. 7.24), we can analyze the energetic requirements to predict the effects of substituents on the stability of the radical intermediates. The a-cleavage reaction of triplet acetone generates an acetyl-methyl radical pair in a process that is 3.5 kcal/mol endothermic and the further loss of CO from acetyl radical is endothermic by 11.0... 

Table 7. Oxidation of ketones with m-chloroperbenzoic acid (49) in the solid state and in chloroform solution3...

The oxidation reaction of ketones by m-chloroperbenzoic acid (49) in the solid state was found to proceed faster than in solution. For example, when a mixture of finely powdered benzophenone and two molar amounts of finely powdered 49 was kept at room temperature for 24 h, phenyl benzoate was obtained in 85 % yield (Table 7) 28). In contrast, the same reaction in chloroform for 24 h gave the same product only... 

The red and orange forms of RhCl[P(C6H5)3]3 have apparently identical chemical properties the difference is presumably due to different crystalline forms, and possibly bonding in the solid. The complex is soluble in chloroform and methylene chloride (dichloromethane) to about 20 g./l. at 25°. The solubility in benzene or toluene is about 2 g./l. at 25° but is very much lower in acetic acid, acetone, and other ketones, methanol, and lower aliphatic alcohols. In paraffins and cyclohexane, the complex is virtually insoluble. Donor solvents such as pyridine, dimethyl sulfoxide, or acetonitrile dissolve the complex with reaction, initially to give complexes of the type RhCl[P(C6H6)3]2L, but further reaction with displacement of phosphine may occur. 

Varma and coworkers reported, for the first time, a simple method for the expeditious reduction of aldehydes and ketones that uses alumina-supported NaBH4 and proceeds in the solid state using microwaves [119]. The process, in its entirety, involves mixing of carbonyl compounds with (10%) NaBH4-alumina and irradiation of the reaction mixture in a household MW oven for 0.5-2 min (Scheme 6.38). 

One of the most attractive features of borohydride reductions is that under micro-wave-enhanced conditions they can be performed in the solid state, and rapidly. We were attracted by the work of Loupy [57], and in particular Varma [58, 59] who has shown that irradiation of a number of aldehydes and ketones in a microwave oven in the presence of alumina doped NaBH4 for short periods of time led to rapid reduction (0.5-2 min) in good yields (62-93%). In our study [60] seven aldehydes and four ketones were reduced (Tab. 13.3). Again reduction was complete within 1 min, the products were of high purity (>95%), of high isotopic incorporation (95%, same as the NaBD4) and the reactions completely selective. 

Metal ketyls are ion-radicals analogous to semiquinone ion radicals and may be considered either oxygen or carbon free radicals. They are readily prepared by treating aromatic ketones with alkali metals in dry ether, benzene, or liquid ammonia under an inert atmosphere.124 125 Benzophenone potassium has been shown to be paramagnetic in the solid state.126... 

Oximes generally demonstrate good stability in the solid state when stored at low temperature. Simple oximes show reasonable stability in neutral aqueous solution but hydrolyze to hydroxylamine and the parent ketone under acidic or basic catalysis [2], As noted, nitro-containing oximes, such as FK409 (9), spontaneously decompose... 

Condensation of [3- or "y-amino alcohols with aldehydes or ketones RR CO gives the product 27. In solution the position of the equilibrium varies with R and R, and with the solvent (73). When the carbonyl reactant is a substituted benzaldehyde, the solid is found (IR, KBr) to comprise molecules of the open-chain structure 27a, whereas aliphatic aldehydes and ketones give crystals of dihydro- 1,3-benzoxazines, 27b. An interesting case is that of the condensation product of o-hydroxybenzylamine with cyclopentanone, for which McDonagh and Smith (73) suggest that ring and chain tautomers coexist in the solid. 

The cyclobutanone 105, on thermolysis at 190°C, undergoes a retro-ene reaction yielding the crystalline 0,y-unsaturated ketone 115. This product in the solid regenerates 105 photochemically, in almost quantitative yield, whereas in solution the diketone 116 is the exclusive photoproduct. The ketone 115 is found in the solid to have the conformation 115a, a conformation that results, presumably, from the requirement for the bulky methyl at C-7 to adopt the pseudo-equatorial rather than the pseudoaxial position. This molecule in fact has a shape... 

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