Catalytic hydrogenation aromatics

Removal of aromatic phenotio groups is accomplished in 65-90% yield by conversion to the sulfonate, followed by catalytic hydrogenation. Aromatic arrrines are deaminated by aprotic diazotlzation with pentyl nitrate in yields up to 89%. ... 

COT is prepared by the polymerization of ethyne at moderate temperature and pressure in the presence of nickel salts. The molecule is non-planar and behaves as a typical cyclic olefin, having no aromatic properties. It may be catalytically hydrogenated to cyclo-octene, but with Zn and dil. sulphuric acid gives 1,3,6-cyclooclairiene. It reacts with maleic anhydride to give an adduct, m.p. 166 C, derived from the isomeric structure bicyclo-4,2,0-octa-2,4,7-triene(I) ... 

Obtained by the catalytic hydrogenation of naphthalene. Owing to the presence of one aromatic ring it can be nitrated and sulphon-ated. It is non-toxic and is used as a solvent for fats, oils and resins. 

Reduction of arenes by catalytic hydrogenation was described m Section 114 A dif ferent method using Group I metals as reducing agents which gives 1 4 cyclohexadiene derivatives will be presented m Section 1111 Electrophilic aromatic substitution is the most important reaction type exhibited by benzene and its derivatives and constitutes the entire subject matter of Chapter 12... 

Aromatic rings in lignin may be converted to cyclohexanol derivatives by catalytic hydrogenation at high temperatures (250°C) and pressures (20—35 MPa (200—350 atm)) using copper—chromium oxide as the catalyst (11). Similar reduction of aromatic to saturated rings has been achieved using sodium in hquid ammonia as reductants (12). 

Reduction. Just as aromatic amine oxides are resistant to the foregoing decomposition reactions, they are more resistant than ahphatic amine oxides to reduction. Ahphatic amine oxides are readily reduced to tertiary amines by sulfurous acid at room temperature in contrast, few aromatic amine oxides can be reduced under these conditions. The ahphatic amine oxides can also be reduced by catalytic hydrogenation (27), with 2inc in acid, or with staimous chloride (28). For the aromatic amine oxides, catalytic hydrogenation with Raney nickel is a fairly general means of deoxygenation (29). Iron in acetic acid (30), phosphoms trichloride (31), and titanium trichloride (32) are also widely used systems for deoxygenation of aromatic amine oxides. 

The y -phenylenediamiaes are easily obtained by dinitrating, followed by catalyticaHy hydrogenating, an aromatic hydrocarbon. Thus, the toluenediamiaes are manufactured by nitrating toluene with a mixture of sulfuric acid, nitric acid, and 23% water at 330°C which first produces a mixture (60 40) of the ortho and para mononitrotoluenes. Further nitration produces the 80 20 mixture of 2,4- and 2,6-dinitrotoluene. Catalytic hydrogenation produces the commercial mixture of diamiaes which, when converted to diisocyanates, are widely used ia the production of polyurethanes (see Amines, aromatic, DIAMINOTOLUENES) (22). 

Catalytic hydtogenation is the most efficient method for the large scale manufacture of many aromatic and ahphatic amines. Some of the commercially important amines produced by catalytic hydrogenation include aniline (from nitrobenzene), 1,6-hexanediamine (from adiponitrile), isophoronediamine (from 3-nitro-l,5,5-trimethylcyclohexanecarbonitrile), phenylenediamine (from dinitrobenzene), toluenediamine (from dinitrotoluene), toluidine (from nitrotoluene), and xyhdine (from nitroxylene). As these examples suggest, aromatic amines ate usually made by hydrogenating the... 

The Zinin reduction is also usehil for the reduction of aromatic nitro compounds to amines in the laboratory. It requires no special equipment, as is the case with catalytic hydrogenations, and is milder than reductions with iron and acid. Usually ammonium or alkah sulfides, hydrosulftdes or polysulftdes are used as the reactant with methanol or ethanol as the solvent. 

The N,]S -dialkyl-/)-PDAs are manufactured by reductively alkylating -PDA with ketones. Alternatively, these compounds can be prepared from the ketone and -lutroaruline with catalytic hydrogenation. The /V-alkyl-/V-aryl- -PDAs are made by reductively alkylating -nitro-, -nitroso-, or /)-aminodipheny1 amine with ketones. The AijAT-dialkyl- PDAs are made by condensing various anilines with hydroquinone in the presence of an acid catalyst (see Amines-aromatic,phenylenediamines). 

Reduction of aryl nitro compounds (Section 22.9) The standard method for the preparation of an arylamine is by nitration of an aromatic ring, followed by reduction of the nitro group. Typical reducing agents include iron or tin in hydrochloric acid or catalytic hydrogenation. 

Catalytic hydrogenation in acetic anhydride-benzene removes the aromatic benzyl ether and forms a monoacetate hydrogenation in ethyl acetate removes the aliphatic benzyl ether to give, after acetylation, the diacetate. Trisubstituted aDcenes can be retained during the hydrogenolysis of a phenolic benzyl ether. ... 

The most notable chemistry of the biscylopen-tadienyls results from the aromaticity of the cyclopentadienyl rings. This is now far too extensively documented to be described in full but an outline of some of its manifestations is in Fig. 25.14. Ferrocene resists catalytic hydrogenation and does not undergo the typical reactions of conjugated dienes, such as the Diels-Alder reaction. Nor are direct nitration and halogenation possible because of oxidation to the ferricinium ion. However, Friedel-Crafts acylation as well as alkylation and metallation reactions, are readily effected. Indeed, electrophilic substitution of ferrocene occurs with such facility compared to, say, benzene (3 x 10 faster) that some explanation is called for. It has been suggested that. 

In much the same vein, the Mannich product from acetophenone with formaldehyde and pyrrolidine (44b) affords procyclidine (49) Dn reaction with cyclohexylmagnesium bromide. In an interesting variation, the ketone is first reacted with phenylmagnesium bromide. Catalytic hydrogenation of the carbinol (50) thus obtained iTin be stopped after the reduction of only one aromatic ring. ... 

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