Coupling mixed

The intermolecular McMurry reaction is first of all a suitable method for the synthesis of symmetrical alkenes. With a mixture of carbonyl compounds as starting material, the yield is often poor. An exception to this being the coupling of diaryl ketones with other carbonyl compounds, where the mixed coupling product can be obtained in good yield. For example benzophenone and acetone (stoichiometric ratio 1 4) are coupled in 94% yield. ... 

Cross coupling of two different carboxylates (= mixed Kolbe electrolysis) is a method for synthesizing unsymmetrical compounds (Eq. 8). As, however, the intermediate radicals combine statistically, the mixed coupling product... 

Table 4. Calculated theoretical yields for mixed coupling products R- R...

Problems due to passivation that lead to an increase of the cell voltage or due to competition by non-Kolbe electrolysis [179] are often less pronounced in mixed coupling. 

Almost all flows in chemical reactors are turbulent and traditionally turbulence is seen as random fluctuations in velocity. A better view is to recognize the structure of turbulence. The large turbulent eddies are about the size of the width of the impeller blades in a stirred tank reactor and about 1/10 of the pipe diameter in pipe flows. These large turbulent eddies have a lifetime of some tens of milliseconds. Use of averaged turbulent properties is only valid for linear processes while all nonlinear phenomena are sensitive to the details in the process. Mixing coupled with fast chemical reactions, coalescence and breakup of bubbles and drops, and nucleation in crystallization is a phenomenon that is affected by the turbulent structure. Either a resolution of the turbulent fluctuations or some measure of the distribution of the turbulent properties is required in order to obtain accurate predictions. 

A Critique ofthe Additivity Principle for Mixed Couples 9... 

The influence of mixed coupling on the properties of Cl Pigment Yellow 12 has been studied recently [12]. Carboxy- or sulpho- substituted derivatives of acetoacetanilide were evaluated as co-coupling components and analysis revealed that the state of the crystal and the particle size were changed and new diffraction peaks were observed. When these modified pigments were treated with a fatty amine such as stearylamine, the hydrocarbon chains enclosed the anionic groups in the co-coupler so that properties such as flowability, wettability and dispersibility in nonpolar solvents were greatly improved. 

A scale of fluorinating ability can be drawn up by deriving the free-energy differences between component couples, (MF — MCl )/n, from HC1/HF ratios. Mixed couples can then be used to derive other values. A heat of formation of PFS was found from the reaction (76)... 

The reaction is considered to proceed via a silyl anion mechanism, although the possibility of a radical-based mechanism has also been discussed.115,125 In order to clarify the mechanism, coupling experiments on a 1 1 mixture of chlorotrimethylsilane, 27 (reduction potential <—3.0 V),126 and chlorotriphenylsilane, 28 (reduction potential vs. standard calomel electrode (SCE) < —3.0 V),120 were performed, in which the mixed coupling product 1,1,1-trimethyl-2,2,2-triphenyldisilane, 29, and the homocoupling product hexaphenyldisilane, 30, only, were found,125 as indicated in Scheme 15. 

Another phenomenon to be detected by X-ray crystallography is the formation of mixed crystals, as observed in the mixed coupling of azo pigments or the solid solutions of quinacridone pigments. A change in the angles of the reflected X-rays of a mixed crystal indicates a transition from one crystal phase to another. If, how-... 

The performance of a pigment which is produced by mixed coupling does not always equal the sum of the characteristics of the individually coupled products. A new crystal modification, for instance, may lead to an unpredictable deviation in the application properties. On a cost-performance basis, the best approach is to add to the reaction mixture traces of a costly coupling component which is known to confer excellent properties on the product, in an attempt to promote a more favorable crystal modification. The resulting mixed product is expected to assume the modification of the trace coupling component and thus to improve its commercial performance without representing a financial strain [7]. 

A loss of the deionized water supply occurred during a workup test. Increased water usage for feed mixing, coupled with reduced membrane capacity while operating with colder water during the winter months, caused the deionized water supply to drop. 

Mixed coupling between naphthalene and alkyl benzenes has also been demonstrated (Table 10, numbers 10-13). The relative yield of mixed coupling products increases with the basicity of the alkyl benzene with mesitylene 19%, with tetramethylbenzene 42%, and with pen-tamethylbenzene 64%. This suggests an electrophilic reaction between naphthalene cation radicals and alkylbenzenes. The mixed coupling reaction of phenan-threne with anisole has been studied kinetically [163]. 

Of interest is the fact that one of the coupling partners in the looplure synthesis was the half acid-half ester (59). Since the ester was untouched in the coelectrolysis, it could potentially function as a site for a second Kolbe oxidation and subsequent coupling. This strategy was utilized in the synthesis of disparlure (67 Scheme 16) [36]. A mixed coupling between the half-acid ester (62) and nonanoic acid (63) (1 10 ratio) proceeded smoothly to afford (64). Saponification... 

An interesting deoxygenation of ketones takes place on treatment with low valence state titanium. Reagents prepared by treatment of titanium trichloride in tetrahydrofuran with lithium aluminum hydride [205], with potassium [206], with magnesium [207], or in dimethoxyethane with lithium [206] or zinc-copper couple [206,209] convert ketones to alkenes formed by coupling of the ketone carbon skeleton at the carbonyl carbon. Diisopropyl ketone thus gave tetraisopropylethylene (yield 37%) [206], and cyclic and aromatic ketones afforded much better yields of symmetrical or mixed coupled products [206,207,209]. The formation of the alkene may be preceded by pinacol coupling. In some cases a pinacol was actually isolated and reduced by low valence state titanium to the alkene [206] (p. 118). 

Mixed coupling can be accomplished by relying on statistics and using the less-costly acid in excess. Prediction of yield of R-R for the reaction ... 

There are many questions still to be answered. What is the role of different metals in the reaction What are the factors governing mixed coupling ... 

Mixed coupling offtuorenone and a, ji-enones. The major products of this reaction arise by conjugate addition of the fluorenone dianion to the enone.1 Examples ... 

The linearized Hamiltonian describing the pairing via the interband scattering of intraband pairs and the vibronic interband mixing (coupling constant V) is written in the form... 

The substitution path b) (Eq. (94) ), is favored by the following experimental conditions low current density, grapliite as anode material, alkaline medium, water or water-pyridine as solvent, and admixture of foreign ions e.g., bicarbonate, sulfate, perchlorate, dihydrogen phosphate, Pb2+, Mn2+, Cu2+, Fe2+, Co2+. The carbonium ion path b) can furthermore be expected for carboxylates RR CHOO with a-substituents R such as alkyl, phenyl 198 hydroxy, halogen 1 amino, or alkoxy. These substituents facilitate oxidation of the intermediate alkyl radical R to the carbonium ion R+. Product formation occurs via carbonium ions and not, as is also conceivable, via mixed coupling of R with Nu ... 

Mixed coupling Nitroethane (H20, KNO2, Ag anode) 1,1-Dinitroethane (82%) 88)... 

Mixed coupling of two different anions, such as sodium azide or nitrite and a sodium salt of a nitroaliphatic compound, can be achieved by coelectrolysis of of both species. Product formation in these cases probably occurs by oxidation of N3 or N02" to the corresponding radical that adds to the nitronate anion to form a radical anion that subsequently is oxidized to product (Eq. (168) ) 161,357). 

Mixed coupling of dissimilar olefins to acetals of substituted aldehydes (Eq. (179)) 384 or unsymmetrical 1,4-dicarbonyl compounds (Eq. (180) ) 384) has also been achieved in fair to good yields. 

The reduction mechanism of carbonyl compounds and its dependence on pH has been outlined in section 8.2. Pinacol formation occurs either by dimerization of the hydroxymethyl radical 101 (Eq. (185) ) or by mixed coupling of 101 with the ketyl 102. Dimerization of 102 seems less probable due to electrostatic repulsion of the two negative charges. Besides coupling, 101 or 102 may be further reduced to the alcohol 103. With active cathodes (e.g., Hg, Sn) 101 forms organo-... 

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