2.5- dimethyl-p-benzoquinone

Examples of this type include the reactions of 2,6-dimethyl-p-benzoquinone with piperylene (Schmidt, C., Sabnis, S. unpublished results referred to in Liu, T. T. H Schmidt, C. Tetrahedron 27, 5289 (1977)) and 6-methoxy-l-vinyl-2,3-dihydronaphthalene (Dickinson, R. A., Kubela, R McAlpine, G. A., Stojanac, Z Valenta, Z. Can. J. Chem. 50, 2377 (1972)), and the reactions of citraconic anhydride with 1-phenyl-butadiene (Alder, K., Haydn, J.,... 

Tsutsumi et al. (1986, 1988) reported photogeneration efficiencies of N-phenylcarbazole (NPCZ) doped polycarbonate containing small concentrations of an electron acceptor 2.6-dimethyl-p-benzoquinone. The thermali-... 

With other quinones, the only olefin yielding stable complexes is 1,5-cyclooctadiene. The quinones employed have been trimethyl-p-benzoquinone, 2,5- and 2,6-dimethyl-p-benzoquinone (531), and vitamin E quinone (530). In general, these complexes show higher water solubility, higher dipole moments, and more marked paramagnetism than do the duroquinone complexes. The paramagnetism suggests that there is some electron transfer from nickel to quinone and that the nickel may indeed have an oxidation state midway between Ni(0) and Ni(II). 

Figure 3. pH dependence of for the electron transfer from cw-[Et2Co(bpy)2] to p-benzoqui-none derivatives in H20-EtOH (5 1 v/v) at 298 K 2,6-dichloro-p-benzoquinone (O) 2,5-dichloro-p-benzoquinone ( ) chloro-p-benzoquinone (A) p-benzoquinone (A) methyl-p-benzoquinone ( ) and 2,6-dimethyl-p-benzoquinone ( ). 

The 1,2-addition of aniline with quinones or ketones to form imines (Schiff bases) is less favorable in aqueous solution than in organic solvent, because the overall equilibrium favors hydrolysis in aqueous or partially aqueous solvents. In the case of sterically hindered quinones in aqueous solution, however, 1,2-addition by aniline is more favorable, and in some instances becomes the dominant mode of attack. As an illustration, 4-methylaniline was reported to undergo both 1,4- and 1,2-addition to 2,6-dimethyl-p-benzoquinone, resulting in a 3 1 product ratio of anilinoquinone to imine (15). 

Diels-Alder reactions with p-quinones (6, 65-66).1 The orientation of Diels-Alder reactions of 6-methoxy-l-vinyl-3,4-dihydronaphthalene (1) with p-quinones is subject to reversal by addition of BF3 etherate (1.3 equivalent). Thus the thermal reaction with 2,6-dimethyl-p-benzoquinone (2) results in exclusive formation of 3, whereas the catalyzed reaction leads predominately to the isomer 4. The adduct 3 is stable to base, but the syn, m-isomer 4 on treatment with Na2C03 is converted to the more stable anti, fran.v-isomcr 5. 

Trimethylphenol (221) was oxidized with dioxygen catalyzed by CuCl2-2H20 to afford 3,5-dimethyl-4-hydroxybenzaldehyde (222) and 2,6-dimethyl-p-benzoquinone (223) in low yields. However, the use of acetone oxime as an additive caused a dramatic change to afford both 222 and 223 in 91.5 and 6.5% yields, respectively . These oxidation products are formed from p-quinone methide 225 through 2,6-dimethyl-4-(hexyloxymethyl)phenol (224) (Scheme 45). 

The proposed reaction mechanism of phenols with O2 catalyzed by Co-amine complexes is shown in Scheme 47. On oxidation of 2,6-dimethylphenol (206) to 2,6-dimethyl-p-benzoquinone (223), magnetic field effects in the cobalt(II)-catalyzed oxidations were examined by using two different high- and low-spin cobalt(II) complexes. The former complex, Co bis(3-(salicylideneamino)propyl)methylamine, Co SMDPT (S = 3/2), displays a maximum increase in the initial rate of ca 1000 G, while the low-spin cobalt complex, Co iV,iV -bis(salicylidene)ethylenediamine, Co salen (S = 1/2), in a 1 10 ratio with pyridine displays a maximum decrease in the initial rate at ca 800 G. The difference in the magnetokinetics of both complexes is explained by magnetic field effects on the singlet-triplet (S-T) radical pair and triplet-triplet (T-T) annihilation reactions... 

Many phenols are oxidized efficiently to quinones by acyl tert-butyl nitroxides in organic solvents. 2,6-Dimethylphenol (206) was oxidized with benzoyl tert-butyl nitroxide in CH2CI2 at room temperature to afford 2,6-dimethyl-p-benzoquinone (223) in 86% yield. Oxidation of 2,4,6-trimethylphenol (221) was also effected with the same reagent in ether to afford the A-fert-butylbenzohydroxamic acid 568 in 98% yield (Scheme 105) . 

Polymethyl 3a,4,7,7a-tetrahydroindoxazenes (77) are obtained by thermal rearrangement of the benzonitrile oxide-hexamethyl-Dewar-benzene cycloadducts (76).90 Reaction of 2,4,6-trimethylbenzonitrile oxide with 3,6-dimethyl-p-benzoquinone yields the 4,7-dioxo-3a,4,7,7a-tetrahydroin-doxazene78(Ar = 2,4,6-Me3C6H2) or its regioisomer, and addition proceeds similarly with 2,6-dimethyl-p-benzoquinone. In a number of other examples, nitrile oxides were found to cycloadd to the C=0 bond of quinones.91... 

Phot, of 2,6-dimethyl-p-benzoquinone -I- 2-propanol KESR 2-propanol 293... 

---