Aromatic ethers, condensation

A. The Basic Series.—In general, aromatic aldehydes condense with aromatic amines in the presence of zinc chloride to form triphenylmethane derivatives (0. Fischer) phenols and phenyl ethers behave similarly in the presence of concentrated sulphuric acid (Baeyer). The products formed are the leuco-compounds of well-known dyes. 

Wordy Over the past few years, we have encountered numerous examples of water as the perfect solvent. We observed this first in osmium-catalyzed dihydroxylation reactions and also in nucleophilic ring-opening reactions of epoxides. We also observed this in cycloaddition reactions and in most oxime ether, hydrazone, and aromatic heterocycle condensation processes.Finally, we observed it in formation reactions of an amide from a primary amine and an acid chloride using aqueous Schotten-Baumann conditions. ... 

Low molecular weight aromatic ethers have been prepared principally by the condensation of phenolate salts with aromatic halides 82). The Ullmann condensation (81), which employs copper or its salts as catalysts has been used in most cases in the laboratory. Recently a modification of the Ullmann condensation which consists of heating copper (1) oxide, the free phenol, and the aromatic halide in s-collidine has been reported (3). This method is recommended for alkali-sensitive aromatic compounds. In addition, reaction of phenolate salts with copper (1) oxide and the aromatic halide in boiling N,N-dimethyl formamide is described. When the halogen is activated by electronegative groups as in -chloroni-... 

Very recently it has been reported that the Friedel-Crafts condensation of aromatic disulfonyl chlorides with aromatic ethers has been successfully effected to yield high molecular weight polymers (20)... 

Reactions of piperazine-2,5-diones with phosphorus pentachloride and phosphorus pentabromide have been described in Sections V.ID and V.IF, respectively. Aromatic aldehydes condense with 3-methylpiperazine-2,5-dione in the presence of acetic anhydride to form mainly mono-A -acetyl derivatives of trans-3-arylidene-6-methylpiperazine-2,5-diones (e.g., 96, R = Ac) (1066). In these products the acetyl group was shown to be attached to position 1 and the 4,5-amide group was found to be sterically hindered. Photolysis formed the cis isomers. Both isomers were deacetylated with methanolic potassium hydroxide (1066). Condensation of 1,4-diacetylpiperazine-2,5-diones with aldehydes has been applied to the synthesis of unsymmetrical 3,6-diarylidenepiperazine-2,5-diones and the reaction has been extended to l,4-diacetyl-3,6-dimethylpiperazine-2,5-diones (1624). Treatment of (96, R = H) with triethyloxonium tetrafluoroborate in dichloromethane gave the monoimino ether, 5-benzylidene-6-ethoxy-3-hydroxy-2-methyl-2,5-dihydropyrazine (97) (1066). l-Methylpiperazine-2,5-dione similarly treated gave 5-ethoxy-l-methyl-2-oxo-l,2,3,6-tetrahydropyrazine (which was condensed with anthranilic acid at 150° to 2-methyl-l,2-dihydropyrazino[2,l-fi]quinazoline-3(4/0.6-dione (98) (1625), and l,4-dimethylpiperazine-2,5-dione gave 5-ethoxy-l,4-dimethyl-2-oxo-1,2,3,4-tetrahydropyrazine and 5,5-diethoxy-l,4-dimethylpiperazin-2-one (1626). 

For polyimides to be useful polymers, they must be processable, which means that they have to be meltable. Melt processability of polyimides can be improved by combining the basic imide structure with more flexible aromatic groups. This can be achieved by the use of diamines that can introduce flexible linkages like aromatic ethers and amides into the backbone. Polyamide-imides (5) are obtained by condensing trimellitio anhydrides and aromatic diamines, while polyetherimides (6) are produced by nitro displacement reaction involving bisphenol A, 4,4 -methylenedianiline, and 3-nitrophthalic anhydride. 

The thermoplastic variety of polyimides with enhanced melt processabihty is obtained by combining the basic imide stmcture with more flexible aromatic groups such as aromatic ethers or amides. Polyamide-imides are produced by condensing trimellitic anhydrides with aromatic diamines, while polyetherimides are made by the reaction between bisphenol A, 4,4 -methylene dianiline, and 3-nitrophthalic anhydride. 

The gaseous products emitted indicate two different crosslinking reactions formation of condensed aromatics by HjS cleavage and reaction with aerial oxygen to aromatic ether bridges. Both reactions result in the slow loss of thermoplastic properties under long-term excessive thermal loading [626]. 

In another report, polyether ketones containing carboranes in the backbone of aromatic units were synthesized by the electrophilic condensation between the ether, l,2-(4-PhOC6H4)2-l,2-C2B10H10, and the dicarboxylic acid, l,2-(4-C02HC6H4)2-l,2-C2BioH,o, with trifluoro-methanesulfo-nic acid (Figure 26.21). This phenylene ether carboranylene ketone (PECK) polymer (54) was found to be extremely thermally stable and showed a much smaller mass loss, up to 1000°C, than was observed for conventional aromatic ether-ketones (Mark and Kenneth, 2002). 

Ullman reaction The synthesis of diaryls by the condensation of aromatic halides with themselves or other aromatic halides, with the concomitant removal of halogens by a metal, e.g. copper powder thus bromobenzene gives diphenyl. The reaction may be extended to the preparation of diaryl ethers and diaryl thio-ethers by coupling a metal phenolate with an aryl halide. 

Miscellaneous Applications. Ben2otrifluoride derivatives have been incorporated into polymers for different appHcations. 2,4-Dichloroben2otrifluoride or 2,3,5,6-tetrafluoroben2otrifluoride [651-80-9] have been condensed with bisphenol A [80-05-7] to give ben2otrifluoride aryl ether semipermeable gas membranes (336,337). 3,5-Diaminoben2otrifluoride [368-53-6] and aromatic dianhydrides form polyimide resins for high temperature composites (qv) and adhesives (qv), as well as in the electronics industry (338,339). 

Polyarylether Ketones. The aromatic polyether ketones are tme thermoplastics. Although several are commercially available, two resins in particular, poly ether ether ketone [31694-16-3] (PEEK) from ICI and poly ether ketone ketone (PEKK) from Du Pont, have received most of the attention. PEEK was first synthesized in 1981 (20) and has been well studied it is the subject of numerous papers because of its potential use in high performance aircraft. Tough, semicrystalline PEEK is prepared by the condensation of bis(4-fiuorophenyl) ketone with the potassium salt of bis(4-hydroxyphenyl) ketone in a diaryl sulfone solvent, such as diphenyl sulfone. The choice of solvent is critical other solvents, such as Hquid HE, promote the reaction but lead to premature low molecular-weight crystals, which do not exhibit sufficient toughness (21). 

This condensation finds considerable generality, enol silyl ethers of a variety of ketones and both aromatic and aliphatic aldehydes are usable For enol silyl ethers of substituted cyclohexanones the reaction is regio- and stereospecific [id]. 

The Fisher oxazole synthesis involves condensation of equimolar amounts of aldehyde cyanohydrins (1) and aromatic aldehydes in dry ether in the presence of dry hydrochloric acid. ... 

Flufenamic acid (162) is a reasonably well-established NSAID (Non Steroidal Anti Inflammatory Drug). Alkylation of its potassiuni salt with the hydroxyethyl ethyl ether of ethylenechlo-rohydrin affords the latendated derivative etofenamate (163) [41]. Antiinflammatory activity is apparently retained when both rings in the fenamate series carry carboxyl groups. Thus, condensation of dichlorobenzoic acid 164 with anthranilic acid (165) by means of nucleophilic aromatic... 

The second step is the condensation reaction between the methylolphe-nols with the elimination of water and the formation of the polymer. Crosslinking occurs hy a reaction between the methylol groups and results in the formation of ether bridges. It occurs also by the reaction of the methylol groups and the aromatic ring, which forms methylene bridges. The formed polymer is a three-dimensional network thermoset ... 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

There have been a number of different synthetic approaches to substituted PTV derivatives proposed in the last decade. Almost all focus on the aromatic ring as the site for substitution. Some effort has been made to apply the traditional base-catalyzed dehydrohalogenation route to PTV and its substituted analogs. The methodology, however, is not as successful for PTV as it is for PPV and its derivatives because of the great tendency for the poly(u-chloro thiophene) precursor spontaneously to eliminate at room temperature. Swager and co-workers attempted this route to synthesize a PTV derivative substituted with a crown ether with potential applications as a sensory material (Scheme 1-26) [123]. The synthesis employs a Fager condensation [124] in its initial step to yield diol 78. Treatment with a ditosylate yields a crown ether-functionalized thiophene diester 79. This may be elaborated to dichloride 81, but pure material could not be isolated and the dichloride monomer had to be polymerized in situ. The polymer isolated... 

For example, there is a dramatic improvement in modulus, tensile strength, and thermal stability when the aliphatic components in polyamides (nylons) are replaced by aromatic components, resulting in polyaramides such as Kevlar (29). Likewise, poly(ether ether ketone) (PEEK), one of the mechanically strongest condensation... 

---