Aryl halides nitration

Today microemulsions are used in catalysis, preparation of submicron particles, solar energy conversion, extraction of minerals and protein, detergency and lubrication [58]. Most studies in the field of basic research have dealt with the physical chemistry of the systems themselves and only recently have microemulsions been used as a reaction medium in organic synthesis. The reactions investigated to date include nucleophilic substitution and additions [59], oxidations [59-61], alkylation [62], synthesis of trialkylamines [63], coupling of aryl halides [64], nitration of phenols [65], photoamidation of fluoroolefins [66] and some Diels-Alder reactions. 

Problem 11.11 Account for the following, (o) Nitration of PhC(CH,), gives only 16% ortho product, whereas PhCH, gives 50%. (ft) Of all the aryl halides, PhF gives the least amount of ortho product on nitration. ... 

An interesting case is provided by the nitration of aryl halides where the effect of the halogen is to deactivate the aromatic nucleus (by the -I effect) but to direct the incoming nitronium ion to the ortho and para positions as a result of the mesomeric interaction of the halogen lone electron pair with the charge developed in the corresponding intermediates [e.g. (5), in the formation of p-bromonitrobenzene from bromobenzene, Expt 6.20],... 

Most reactions such as halogenation, nitration, sulphonation etc. are reactions with a positive ion, with an electrophilic reagent therefore, in which the aromatic molecule reacts nu-cleophilically. In hydrolysis, alcoholysis and aminolysis of aryl halides the reagents are nucleophilic. Radical reactions are also possible, especially in the gas phase at higher temperatures. 

The electrophilic aromatic substitution of aryl halides takes place less readily than with benzene (electron-withdrawing effect), but occurs at the ortho and para positions (the lone pairs on the halogen assist in delocalizing the positive charge in the intermediate). Further chlorination of chlorobenzene, in the presence of aluminium or iron trichlorides, gives 1,4-dichlorobenzene and some 1,2-dichlorobenzene. Nitration normally occurs to give the 2- and 4-nitro- and 2,4-dinitrochlorobenzenes (Scheme 4.13). 

Nitration. Add 0.4 mL of concentrated sulfuric acid to 100 mg of the aryl halide (or aromatic compound) and stir. Add 0.4 mL of concentrated nitric acid dropwise with stirring and shaking while cooling the reaction mixture in water. Then heat and shake the reaction mixture in a water bath at about 50°C for 15 min, pour into 2 mL of cold water, and collect the product by filtration. Recrystallize from methanol to constant melting point. 

Aryl halides are distinguished from aromatic hydrocarbons by the presence of halogen, as shown by elemental analysis. Aryl halides are distinguished from most alkyl halides by their inertness toward silver nitrate in this respect they resemble vinyl halides (Sec. 25.5). 

The chemical reactivity of the thiocyano groups in these chelate rings has not been investigated, but the halogen atoms in the 3-halo metal acetylacetonates have been found to be quite inert and their behavior is different from that of aryl halides, since treatment of the tris(3-bromo-2,4-pentanediono)chromium(III) chelate with magnesium or lithium in benzene or tetrahydrofuran resulted in no reaction. Attempted nucleophilic displacement of the bromine atoms in this chelate by azide, acetate, nitrate, and iodide ions in hot dimethylformamide also failed. In most of these... 

Reactions of Pyrroles. 1,3-Di-t-butylpyrrole forms the first stable protonated pyrrole, the salt (104). Electrophilic substitution of pyrrole with MeaC or Me FC in the gas phase occurs mainly at the j3-position, as does nitration and Friedel-Crafts acylation of l-phenylsulphonylpyrrole2 Pyrrole-2,5-dialdehyde has been prepared by Vilsmeier-Haack formylation of the ester (105), followed by hydrolysis. A similar method has been used to convert the di-acetal (106) into pyrrole-2,3,5-tricarbaldehyde. AT-Benzoyl-pyrrole reacts with benzene in the presence of palladium(II) acetate to yield a mixture of l-benzoyl-2,5-diphenylpyrrole, the bipyrrolyl (107), and compound (108). Treating lithiated A-methylpyrrole with nickel(II) chloride results in the polypyrrolyls (109 = 0-4). 2-Aryl-1-methylpyrroles are obtained by cross-coupling of l-methylpyrrol-2-ylmagnesium bromide with aryl halides in the presence of palladium(0)-phosphine complexes. ... 

SULFICYLBIS (METHANE) (67-68-5) CjHjOS (CH3)2S0 Combustible liquid [explosion limits in air (vol %) 2.6 to 63.0 flashpoint 203°F/95°C oc autoignition temp 419°F/215°C Fire Rating 2]. Violent or explosive reaction with strong oxidizers, acryl halides, aryl halides and related compounds, alkali metals p-bromobenzoyl acetanilide, boron compounds, especially hydrides iodine pentafluoride, magnesium perchlorate, methyl bromide, perchloric acid, periodic acid, silver fluoride, sodium hydride, potassium permanganate. Forms powerfully explosive mixtures with metal salts of oxoacids [iron(III)nitrate, phosphonic acid, sodium perchlorate]. On small fires, use dry chemicals or COj extinguishers. 

For fast reactions of the type represented by reaction 13.2, carried out under the conditions stated earlier, micromixing becomes the dominant consideration. However, studies on the effect of micromixing in such reactions are sparse. Some examples are as follows nitration of aromatic componds in general (Schofield, 1980), potassium metal-provoked reactions of aryl halides with amide and acetone enolate ions (Tremelling and Bunnett, 1980X coupling of 1-naphthol with diazotized sulfanilic acid (Bourne et al., 1981, 1985), reactions of o-(3-butenyl)-halobenzenes and 6-bromo-1-hexene with alkali metals in ammonia/terr-butyl alcohol solution (Meijs et al., 1986), and monoacylation of symmetrical diamines (Jacobson et al., 1987). In some fast reactions, hydrogen ions are produced. 

In aryl halides and vinyl halides the C - X bond is very strong, as the lone pair of electrons on halogen atom gets delocalized which gives the C - X bond, partial double bond character. Moreover, the C-X bond is formed by sp - p orbital overlap. This makes the bond short and strong. Thus, it is very difficult to cleave the C-X bond of aryl and vinyl halides and they do not give white precipitate with silver nitrate solution. 

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