Dehydrative aromatization

Barrett and co-workers adapted ring-opening metathesis polymerization (ROMP) to prepare the ROMPgel TosMlC reagent 1621 (Scheme 1.414, p. 364). Thus copolymerization of the norbornene-derived formamide 1620 with norbor-nene in the presence of Grubbs s catalyst" gave 1621 in quantitative yield after dehydration. Aromatic aldehydes react with 1621 in the presence of a strong... 

Tamura and colleagues generated an IQD (16) from 3-carboxy-l-methylindole-2-acetic anhydride by treatment with sodium hydride. Subsequent trapping with acetylenic dienophiles and a chloroquinone afforded the expected cycloadducts (Scheme 9, equation 1, and 17, 18) [65]. Ila, Junjappa, and coworkers also employed basic conditions to generate and trap a bright red IQD (19) from 1,2-dime-thyl-3-carboxyaldehyde (equation 2) [66]. A large number of carbazoles (20-22) and 1,2-dihydrocarbazoles (23-25) were synthesized in very good yields. Either silica gel or pyridinium tosylate was required to dehydrate/aromatize the initially formed carbinol intermediate. 

Methyl-l-phenylhept-3-yne-2,6-diol undergoes a one-pot three-step cascade reaction with alkyl and aryl aldehydes to provide 2,4-dihydro-lH-benzo[ isochromans.This two-component cascade reaction promoted by Bp3-OEt2 involves an alkynyl-Prins cyclization, Friedel-Crafts arylation, and dehydrative aromatization (130L4070). Other Prins cascade cycliza-tions of 2-arylethylbut-3-en-l-ol with aliphatic and aromatic aldehydes occur in the presence of Sc(OTf)3 andp-TsOH to prepare trans-fused hexa-hydro-1 H-benzo[ isochromans in good yields and excellent selectivity (Scheme 44) (13EJ01993). 

And, if we were able to block, or simply ignore, position 2, we would still have to concern ourselves with the potential competitive endocyclic and exocyclic enolization (positions 6 vs 20. A final consideration that could limit or restrict reaction conditions was that Ae desired hydroxylation-at position 6--would provide a product Aat is technically a hydrate of 2,6-dihydroxyacetophenone homolog, and facile dehydration-aromatization of 11 (R = 10-phenyldecyl) to Ae related... 

We evaluated the catalytic performance of the arylsulfonic acid MELS in a number of reactions, including isomerization of butenes, MTBE synthesis, methanol dehydration, aromatic alkyMon, and MTBE cracking. An example of its utilization as a catalyst for MTBE synthesis follows. 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

By dehydration of aromatic amides with phosphorus pentoxide, for example ... 

Lithiated indoles can be alkylated with primary or allylic halides and they react with aldehydes and ketones by addition to give hydroxyalkyl derivatives. Table 10.1 gives some examples of such reactions. Entry 13 is an example of a reaction with ethylene oxide which introduces a 2-(2-hydroxyethyl) substituent. Entries 14 and 15 illustrate cases of addition to aromatic ketones in which dehydration occurs during the course of the reaction. It is likely that this process occurs through intramolecular transfer of the phenylsulfonyl group. 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

A simpler nonphosgene process for the manufacture of isocyanates consists of the reaction of amines with carbon dioxide in the presence of an aprotic organic solvent and a nitrogeneous base. The corresponding ammonium carbamate is treated with a dehydrating agent. This concept has been apphed to the synthesis of aromatic and aUphatic isocyanates. The process rehes on the facile formation of amine—carbon dioxide salts using acid haUdes such as phosphoryl chloride [10025-87-3] and thionyl chloride [7719-09-7] (30). 

Organic Reactions. Nitric acid is used extensively ia iadustry to nitrate aHphatic and aromatic compounds (21). In many iastances nitration requires the use of sulfuric acid as a dehydrating agent or catalyst the extent of nitration achieved depends on the concentration of nitric and sulfuric acids used. This is of iadustrial importance ia the manufacture of nitrobenzene and dinitrotoluene, which are iatermediates ia the manufacture of polyurethanes. Trinitrotoluene (TNT) is an explosive. Various isomers of mononitrotoluene are used to make optical brighteners, herbicides (qv), and iasecticides. Such nitrations are generally attributed to the presence of the nitronium ion, NO2, the concentration of which iacreases with acid strength (see Nitration). 

Nitio olefins can be made in some cases by dehydration of the aromatic nitrohydroxy derivatives. Subsequent reduction yields the aromatic amine. The following three-step reaction yielding 2-amino-l-phenylbutane illustrates the synthesis of this class of valuable pharmaceutical compounds. 

Methylphenol. This phenol, commonly known as o-cresol, is produced synthetically by the gas phase alkylation of phenol with methanol using modified alumina catalysis or it may be recovered from naturally occurring petroleum streams and coal tars. Most is produced synthetically. Reaction of phenol with methanol using modified zeoHte catalysts is a concerted dehydration of the methanol and alkylation of the aromatic ring. 2-Methylphenol [95-48-7] is available in 55-gal dmms (208-L) and in bulk quantities in tank wagons and railcars. 

Etherification. Ethers of amyl alcohols have been prepared by reaction with ben2hydrol (63), activated aromatic haUdes (64), dehydration-addition reactions (65), addition to olefins (66—71), alkoxylation with olefin oxides (72,73) and displacement reactions involving thek alkah metal salts (74—76). 

Oxa2oles react with dienophiles to give pyridines after dehydration or other aromatization reactions (69,70). A commercially important example is the reaction of a 5-aLkoxy-4-methyloxa2ole with 1,4-butenediol to yield pyridoxine (55), which is vitamin... 

The largest use of NMP is in extraction of aromatics from lube oils. In this appHcation, it has been replacing phenol and, to some extent, furfural. Other petrochemical uses involve separation and recovery of aromatics from mixed feedstocks recovery and purification of acetylenes, olefins, and diolefins removal of sulfur compounds from natural and refinery gases and dehydration of natural gas. 

Sulfonic acids may be subjected to a variety of transformation conditions, as shown in Figure 2. Sulfonic acids can be used to produce sulfonic anhydrides by treatment with a dehydrating agent, such as thionyl chloride [7719-09-7J. This transformation is also accomphshed using phosphoms pentoxide [1314-56-3J. Sulfonic anhydrides, particulady aromatic sulfonic anhydrides, are often produced in situ during sulfonation with sulfur trioxide. Under dehydrating conditions, sulfonic acids react with substituted aromatic compounds to give sulfone derivatives. 

The reaction is irreversible and can be used to synthesize aUphatic and aromatic esters. In addition, there are no complications involving water removal or azeotrope formation. Boron tribromide can be used ia place of boron trichloride, but the bromide has a stronger tendency to halogenate the alkyl group of the alcohol (26). Boron tritiuoride does not give the ester, but gives either a complex or dehydrated product. 

This reaction was also extended to other aromatic aldehydes for the preparation of a,P unsaturated carboxyUc acids. Several mechanisms of the reaction have been proposed (45). The most accepted mechanism iavolves the reaction of the aldehyde with the enol form of the acid anhydride which is promoted by the presence of the sodium salt or of another base. The resulting reaction product is then dehydrated iato an unsaturated carboxyUc acid. 

Properties of ferrocene-containing polymers have been improved by inclusion of pyrazole systems in the backbone. The synthesis of (748) was achieved by condensation of bis()3-diketoferrocenes) with aromatic dihydrazines to give polyhydrazones that were later cyclo-dehydrated (B-80MI40408). 

---