Nucleophilic Route

The nucleophilic route seems to be favored by industrial processes. Polymers are prepared from dichlorobenzonitrile, aromatic diols such as resorcinol, HQ, and biphenol. The reaction proceeds in polar solvents using a base as a catalyst.  

For example, 2,6-dichlorobenzonitrile, and a mixture of 2,7-diby-droxynaphthalene, and hydroquinone, with a slight stoichiometric excess of the hydroxy compound is condensed at 160-190°C in an inert atmosphere. Potassium carbonate is used as a catalyst and a mixture of sulfolane and toluene is used as a solvent.  

With 1,3-dimethylimidazolidinone as a solvent, higher condensation temperatures can be reached. Higher molecular weights are also obtained, therefore 1,3-dimethylimidazolidinone is favored as a solvent. Monovalent nitriles, such as 2-fluorobenzonitrile, act as a molecular weight regulation agent  

3 Aryl Carbonate Cyano Arylene Ether Copolymers 

Arylene carbonate cyanoarylene ether copol5miers can be prepared by the reaction of a solution of a bisphenolic capped cyanoarylene ether oligomer with phosgene in the presence of a base. The reaction with phosgene is carried out in an inert atmosphere. The pol5mierization reaction is carried out at a subambient temperature so that the reaction proceeds at a controllable rate. ° The materials are useful as gas separation membranes. 

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The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

OS 49] [R 17] [R 26] [P 36] At almost quantitative conversion, yields of 90% of two (in a first run) unidentified products and of 10% N,N -diethylurea were reported, accompanied by small amoimts of the mono-product [38], AH products no longer contained any C=S moiety, hence were somehow attacked via a nucleophilic route. By subsequent MS and IR analysis, the two main products were identified as N,N -diethyl-N-nitrosourea and, probably, N,N -diefhyl-N,N -dinitrosourea. By optimization of the [P 23] procedure, 100% selectivity for the nitration of N,N -diethylurea to N,N -diethylurea was achieved. 

Obviously, in such cases the CD is acting as a true catalyst in esterolysis. The basic cleavage of trifluoroethyl p-nitrobenzoate by a-CD occurs by both pathways approximately 20% by nucleophilic attack and approximately 80% by general base catalysis (GBC) (Komiyama and Inoue, 1980c). The two processes are discernible because only the former leads to the observable p-nitrobenzoyl-CD. For the ester, Ks = 3.4 mM and kjka = 4.4 for the GBC route (1.25 for the nucleophilic route), and so KTS = 0.77 mM. For reaction within the ester CD complex [28], it was estimated that the effective molarity of the CD hydroxyl anion was 21-210 m (for Br0nsted /3 = 0.4 to 0.6 for GBC). Such values are quite reasonable for intramolecular general base catalysis (Kirby, 1980). 

The nucleophilic route In this method a sulfur nucleophile is made to react with an electrophilic species generated by suitable means from the piperazinedione. The method can therefore be subdivided into different classes, depending on the electrophile used. 

Depending on biological results on the prostaglandin EP3 receptor a larger set of compounds could easily be obtained using other amines or N-nucleophiles (route a) or terminal alkenes (route b) or cuprates (both routes) ... 

Two general methods, electrophilic and nucleophilic, predominate the synthesis PAEKs [153,154]. The nucleophilic route to PAEKs was used in the polymerization of various combinations of bis-electrophiles... 

Figure 1. Structures of precursors for nucleophilic routes to deoxyfluorohexoses.

Nucleophilic Route Hydroxy Functional Monomer Halogen Functional Monomer... 

The nucleophilic route employs hydroquinone and 4,4 -dihalobenzophe-none with a base as a catalyst, in solvents, such as iV-methyl-2-pyrrolidone (NMP) or sulfolane. For example, PEEK is manufactured by the reaction of 4,4 -difluorodiphenyl ketone with the potassium salt of hydroquinone, as shown in Figure 6.3. 

The nucleophilic route can be improved, by using diphenyl sulfone as a high-boiling solvent." In this process, hydroquinone is transformed into its dipotassium salt by heating with an equivalent amount of potassium carbonate or potassium bicarbonate, with simultaneous removal of the water at 150-200°C, followed by the addition of the second monomer, namely, 4,4 -difluorobenzophenone. The polymerization reaction is carried out at 320-350°C to obtain a polymer of an IV in the range of 0.8 to 1.4 dl g with a melting point of 335-350°C. The polymers by this process are claimed to be very useful for wire coating. ... 

Similarly to poly(ether ketone)s (PEK)s, PENs have been prepared according to a nucleophilic route and an electrophilic route. 

The nucleophilic route can be improved, by using diphenyl sulfone as a high-boiling solvent [3]. In this process, hydroquinone is transformed into its dipotassium salt by heating with an equivalent amount of potassium carbonate or potassium bicarbonate, with simultaneous removal of the water at 150-2(X)°C,... 

The addition of elemental [ Fjfluorine to 2-(2-nitro-l[H]-imidazol-lyl)-N-(2,3,3-trifluoroallyl)-acetamide in trifluoroacetic acid to form [ F]EF5 represents a more recent example of an aliphatic electrophilic fluorination (Dolbier et al. 2001, cf O Fig. 42.3). EF5 as well as EFi (Kachur et al. 1999) and EF3 (Josse et al. 2001), which are prepared via nucleophilic routes, have been suggested for PET imaging of tumor hypoxia. 

Monomer (29) has two chlorine atoms that differ considerably in their reactivity toward zero-valent nickel. The chlorine in the para position to the sulfone group should react first it is, therefore, expected that the final polymer will have structure (30). Polymer (30) can also be synthesized via the nucleophilic route by polycondensing 4,4 -bis(p-chlorophenylsulfonyl) biphenyl (31) with 4,4 -biphenol (32) [equation (VIII)] ... 

The data in Table IV show that the properties of the two materials, i.e. (30) made via the nickel coupling route [equation (VII)] and (30) made via the nucleophilic route [equation (VIII)] are practically identical. 

Figurel.2 Nucleophilic routes to PEEK, PEK, PEEKK, PEKEKK, PEKK [2, 5]...

One drawback of the nucleophilic routes described so far is that they produce a metal salt and solid solvent residue which needs to be removed from the system. In many condensation polymerisations the small molecule produced is volatile and can be removed directly from the reaction. The KF residue leads to reversibility of the reaction and transetherification. However, the low solubility of KF in diphenylsulfone means that a high molecular weight can still be achieved and the KF can be removed by extraction with water. Indeed extraction with water at very high temperatures has recently been used to produce ultrahigh-purity grades of PEEK [10]. These materials can have less than 1 ppm residual potassium and sodium. 

In the past electrophilic PEK and PEKEKK have been produced by Raychem and BASF, respectively. Currently the vast majority of the world s supply of PAEK is made by nucleophilic routes. However, recent commercial electrophilic products include PEKK and Gharda s Gatone PEEK technology - which is now owned by Solvay. PAEK produced by these processes do not have fluorine end groups. 

PEKK is produced from diphenylether and phthaloyl chlorides [19]. It is one of the few PAEK that would be difficult to make by nucleophilic routes because of the obvious complexity of the monomer required. The high melting point of linear, 100% para PEKK means that commercial PEKK is actually made from both terphthaloyl (T) and isophthaloyl chloride (I). Crystalline PEKK is typically 80 20 T/I whereas the amorphous grades used for thermoforming are 60 40 T/I. 

Method of synthesis nucleophilic route, ketimine route, or electrophilic process PEK can be obtained by reaction of 4,4 -difuorobenzophenone with 4,4 -dihydroxybenzophenone in the presence of potassium carbonate, using diphenyl sulfone as solvent Ben-Halda, A Colquhoun, H M Hodge, P Williams, D J, J. Mater. Chem., 10, 2011-16, 2000. 

The Petasis reaction represents a boronic acid variant of the Mannich reaction, and therefore is also referred to as a borono-Mannich reaction. It was first explored with formaldehyde as the carbonyl component and alkenyl, or ot,p-unsaturated organoboronic acid (III) as a nucleophile (route a in Scheme 8.2) [13]. It was later developed in a practical synthesis of a-amino acids (VI) from ot-keto acids (IV) and alkenyl boronic acids (III) [14] (route b in Scheme 8.2). 

Ng et al. described the use of less expensive and industrially far better available epichlorohydrine instead of the bromo derivative, but in the experience of the authors of this book the synthesis could not be reproduced in good yields. Another nucleophilic route to EDOT-CH2OH, very similar to the scheme in Figure 12.2, utilizes l-acetoxy-2,3-dibromopropane instead of epibromohydrin (Figure 12.3). Although formation of the undesirable isomer ProDOT-OH is omitted, the synthesis suffers from low yields (about 25%) in the nucleophilic substitution step. ... 

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