Ethers, aromatic

Diphenyl ethers show peaks at M — H, M — CO, and M - CHO by complex rearrangements/ 

Thioalcohols, also called mercaptans, correspond to the general formula R—S—H. The 

Ethyl mercaptan C2H5SH, propyl mercaptan C3H7SH, butyl mercaptan C4H9SH, amyl mercaptan C5H11SH. 

Mercaptans have no action on aluminium, even at high temperatures. Certain of their derivatives are prepared at elevated temperatures in reactor vessels made of aluminiiun alloy. An example is sulphonal, which does not attack aluminium at 125 °C. 

Thiophenols, like mercaptans, have no action on aluminium. Benzyl sulphide (C6HsCH2)2S is a corrosion inhibitor for aluminium in acid medium. 

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This reagent affords compounds (1 1) with aromatic hydrocarbons and other classes of organic compounds (heterocyclic compounds, aromatic ethers, etc.). 

Oxidation of side chains. The oxidation of halogenated toluenes and similar compounds and of compounds with side chains of the type —CHjCl and —CH OH proceeds comparatively smoothly with alkaline permanganate solution (for experimental details, see under AromcUic Hydrocarbons, Section IV.9,6 or under Aromatic Ethers, Section IV,106). The resulting acid may be identified by a m.p. determination and by other teats (see Section IV,175). 

Purely aromatic ethers e.g., diphenyl ether), which are commonly encountered, are very hmited in number. Most of the aromatic ethers are of the mixed aliphatic - aromatic type. They are not attacked by sodium nor by dilute acids or alkahs. When hquid, the physical proper-ties (b.p., d . and ) are useful constants to assist in their identification. Three important procedures are available for the characterisation of aromatic ethers. 

Cleavage with hydriodic acid. Aromatic ethers undergo fission when heated with constant boihng point hydriodic acid ... 

Sulphonamides of aryl ethers. Aromatic ethers react smoothly in chloroform solution with chlorosulphonic acid at 0° to give suljihonyl chlorides, for example ... 

Picrates of aromatic ethers. Most phenohc ethers react with picric acid in chloroform or alcoholic solution to yield crystalUne picrates (compare At oTnatic Hydrocarbons, Section IV,9,1). 

Dissolve 0 01 mol of the phenohc ether in 10 ml. of warm chloroform, and also (separately) 0 01 mol of picric acid plus 5 per cent, excess (0 -241 g.) in 10 ml. of chloroform. Stir the picric acid solution and pour in the solution of the phenohc ether. Set the mixture aside in a 100 mb beaker and ahow it to crystallise. Recrystahise the picrate from the minimum volume of chloroform. In most cases equahy satisfactory results may be obtained by conducting the preparation in rectified spirit (95 per cent. CjHgOH). The m.p. should be determined immediately after recrystallisation. It must be pointed out, however, that the picrates of aromatic ethers suflFer from the disadvantage of being comparatively unstable and may undergo decomposition during recrystaUisation. 

Table IV, 106 contains data referring to a number of selected aromatic ethers.

The mixed aliphatic - aromatic ethers are somewhat more reactive in addition to cleavage by strong hydriodio acid and also by constant b.p. hydrobromio acid in acetic acid solution into phenols and alkyl halides, they may be bromi-nated, nitrated and converted into sulphonamides (Section IV,106,2). 

Aromatic carbon Aromatic compounds Aromatic esters Aromatic ethers... 

Solvent for Displacement Reactions. As the most polar of the common aprotic solvents, DMSO is a favored solvent for displacement reactions because of its high dielectric constant and because anions are less solvated in it (87). Rates for these reactions are sometimes a thousand times faster in DMSO than in alcohols. Suitable nucleophiles include acetyUde ion, alkoxide ion, hydroxide ion, azide ion, carbanions, carboxylate ions, cyanide ion, hahde ions, mercaptide ions, phenoxide ions, nitrite ions, and thiocyanate ions (31). Rates of displacement by amides or amines are also greater in DMSO than in alcohol or aqueous solutions. Dimethyl sulfoxide is used as the reaction solvent in the manufacture of high performance, polyaryl ether polymers by reaction of bis(4,4 -chlorophenyl) sulfone with the disodium salts of dihydroxyphenols, eg, bisphenol A or 4,4 -sulfonylbisphenol (88). These and related reactions are made more economical by efficient recycling of DMSO (89). Nucleophilic displacement of activated aromatic nitro groups with aryloxy anion in DMSO is a versatile and useful reaction for the synthesis of aromatic ethers and polyethers (90). 

Like other aromatic compounds, aromatic ethers can undergo substitution in the aromatic ring with electrophilic reagents, eg, nitration, halogenation, and sulfonation. They also undergo Eriedel-Crafts (qv) alkylation and acylation. 

Aromatic ethers 11.5-N -140.04-1- 13.869N The AN value is not a correction to regular ether value, but the AB value is a correction to regular etheF... 

If the compound has an aromatic----OH or------NH2, or if there is an aromatic ether, use AN contribution in table but neglect other substituents on the ring such... 

H-Bond Acceptor (HBA) Acyl chlorides Acyl fluorides Hetero nitrogen aromatics Hetero oj gen aromatics Tertiary amides Tertiary amines Other nitriles Other nitros Isocyanates Peroxides Aldehydes Anhydrides Cyclo ketones Ahphatic ketones Esters Ethers Aromatic esters Aromatic nitriles Aromatic ethers Sulfones Sulfolanes... 

TRAHANOVSKY Ether oxidation Oxidation of aromatic ethers to carbonyl compounds with cemim ammonium nitrate... 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

Vinyl butyl ether 9.4 Aromatic Ethers Methyl phenyl ether (anisole) 255 437 22... 

Observable Characteristics - Physical State (as slupped) Liquid Color Colorless to pale yellow Odor Aromatic ethereal characteristic. 

Residual aromatic ether concentrations are determined from the absorbance at 278 mfi of the crude reduction products in methanol solution. Steroidal ether concentrations of 1 mg/ml are employed. The content of 1,4-dihydro compound is determined, when possible, by hydrolysis to the a, -unsaturated ketone followed by ultraviolet analysis. A solution of the crude reaction product (usually 0.01 mg/ml cone) in methanol containing about 1/15 its volume of water and concentrated hydrochloric acid respectively is kept at room temperature for 2 to 4 hr. The absorbance at ca. 240 mfi is measured and, from this, the content of 1,4-dihydro compound can be calculated. Longer hydrolysis times do not increase the absorbance at 240 mp.. 

In the Schmidt reaction of fluonnated dicarboxyhc acids, the appropnate amides can be obtained in fairly good yield [48] Complications arise from possible cychzation if the fluorine atom is in the 8 position relative to the newly formed amino group [/] Fluonnated aromatic ethers, upon heating in dimethylformamide, undergo Smiles rearrangement to give diarylamines [49, 50] (equation 11)... 

A number of examples of the use of molten pyridinium chloride (mp 144 °C) in chemical synthesis are known, dating back to the 1940 s. Pyridinium chloride can act both as an acid and as a nucleophilic source of chloride. These properties are exploited in the deallcylation reactions of aromatic ethers [4]. An example involving the reaction of 2-methoxynaphthalene is given in Scheme 5.1-2 [16, 18], and a mechanistic explanation in Scheme 5.1-3 [18]. 

In general most of the commercial polymers are not comparable to metals and ceramics in terms of load-bearing property, mechanical strength, and thermal stability. To overcome these difficulties the aromatic ether or sulfide (thioether) linkages in the polymer backbone... 

Loss of CH20 from simple aromatic ethers... 

The positive bromination of aromatics ethers was first studied by Bradfield et al.193 and by Branch and Jones194. The reaction of hypobromous acid in 75 % aqueous acetic acid with benzyl 4-nitrophenyl ether and 4-nitrophenetole at 20 °C was very rapid and approximately second-order193. The value of k2/[H+] remained constant in the [H+] range 0.005-0.090 M for the effect of added mineral acids on the bromination of 4-nitroanisole and 4-nitrophenetole (at 19.8 °C)194. The variation in reaction rate with the percentage of acetic acid in the medium was also studied and showed a large increase in the 0-10 % range with a levelling off at approximately 25 % acetic acid (Table 52) this was attributed... 

Bradfield et al.21g first studied the kinetics of molecular bromination using aromatic ethers in 50% aqueous acetic acid at 18 °C. They showed that the kinetics are complicated by the hydrogen bromide produced in the reaction which reacts with free bromine to give the tribromide in BrJ, a very unreactive electrophile. To avoid this complication, reactions were carried out in the presence of 5-10 molar excess of hydrogen bromide, and under these conditions second-order rate coefficients (believed to be I02k2 by comparison with later data) were obtained as follows after making allowance for the equilibrium Br2 + Br7 Bn, for which K = 50 at 18 °C 4-chloroanisole (1.12), 4-bromoanisole (1.20), 4-... 

A number of workers have measured rates of dedeuteration of aromatic ethers in this medium (Table 172). The agreement between the different sets of work is poor in the case of anisole and good otherwise. The result of Lauer and Day5 6 6 for dedeuteration at 80 °C is probably the most suspect certainly one would not expect such large differences in activation energy for reaction at the ortho and... 

Reaction is brought about thermally usually at around 200 °C either in an inert solvent (diphenyl ether, cyclohexane and diethylaniline have been used) or in the absence of a solvent. If the ortho positions in the aromatic ether are blocked (as in LXXVII) then rearrangement to the para position LXXVIII occurs, viz. 

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