Hydrogenation anisole

The hydrogenation of arenes is performed at room temperature and under 40 bar of H2. In all cases, the conversion is complete after a few hours. 3000 TTO are demonstrated for anisole hydrogenation in 45 h (Scheme 5). 

The polyoxoanion-stabilized Rh(0) nanoclusters were investigated in anisole hydrogenation [6,95]. The catalytic reactions were carried out in a single phase... 

Table 11.4 Influence of the ratio TOA/Rh on conversion and selectivity in 2-methyl-anisole hydrogenation reaction after24h.

When a solution of a diazonium compound in absolute methanol is boiled, the chief product is the corresponding methyl ether, henzenediiizonium hydrogen sulphate thus giying methyl phenyl etlier or anisole ... 

Heat under reflux i g. of anisole and 10 ml. of constant-boiling hydrogen iodide for 30 minutes. Now distil off the volatile methyl iodide and identify it in the distillate (see pp. 390-391). 

Depending on the ring substituent, trifluoromethoxyben2enes can be made by the sequential chlorination—fluorination of anisole(s) (351—354). A one-step process with commercial potential is the BF (or SbF2)-cataly2ed reaction of phenol with carbon tetrachloride/hydrogen fluoride (355). Aryl trifluoromethyl ethers, which may not be accessible by the above routes,may be made by fluorination of aryl fluoroformates or aryl chlorothioformates with sulfur tetrafluoride (348) or molybdenum hexafluoride (356). 

Benzylsulfonamides, prepared in 40-70% yield, are cleaved by reduction (Na, NH3, 75% yield H2, Raney Ni, 65-85% yield, but not by H2, Pt02) and by acid hydrolysis (HBr or HI, slow). They are also cleaved by photolysis (2-4 h, 40-90% yield). The similar p-methylbenzylsulfonamide (PMS—NR2) has been prepared to protect the e-amino group in lysine it is quantitatively cleaved by anhydrous hydrogen fluoride/anisole (—20°, 60 min). Another example of this seldom used group is illustrated below... 

Robertson et al.261 measured rates of bromination of some aromatic hydrocarbons in acetic acid containing sodium acetate (to eliminate protonation of the aromatic by liberated hydrogen bromide) and lithium bromide (to reduce the rate to a measurable velocity ) at 25 °C, the second-order rate coefficients for 3-nitro-N,N-dimethylaniline and anisole being 14.2 and 0.016 respectively the former compound was thus stated to be about 1012 times as reactive as benzene (though no measurement of the latter rate coefficient, inferred to be 1.33 xlO-11, could be found in the literature) and this large rate spread gives one further indication of the unreactive nature of the electrophile. Other rates relative to benzene were ... 

Scheme 4 Hydrogenation of anisole by polyoxoanion-stabilized Rh(0) nanocluster catalyst...

A similar result is obtained with 30 equivalents of H2O added but a long reaction time is required namely 215 h. Nevertheless, in all cases a black precipitate of bulk Rh(0) is visible at the end of the reaction justifying the destabilization of nanoclusters due to the interaction of H or H2O with the basic P2Wi5Nb3062 polyoxoanion. Finally, the partial hydrogenation of anisole to yield 1-methoxycyclohexane (up to 8%) with a soluble nanocluster catalyst has been reported by Finke and coworkers (see Sect. 3). 

---