Chlorine precursor route

Since the products often precipitate during the polymerization, a modification was reported by Swatos et al. [82] involving the use of only about one equivalent of f-BuOK. This method, the so-called chlorine precursor route , first gives a soluble non-conjugated precursor (66) which is then converted thermally in the film or in a high boiling solvent, e.g. cyclohexanone. In the latter case, homogeneous solutions of (soluble) PPV derivatives 63 can be obtained. 

J. N. Wilking, B. Hsieh, and G. A. Arbuckle-Keil. Chlorine precursor route to poly(2-phenoxy p-phenylene vinylene) Synthesis and characterization. Synth. Met., 149(l) 63-72, February 2005. 

PPV and PPV derivatives have been synthesized using precursor routes because the final highly conjugated product is insoluble and intractable. The advantage of the precursor route is that the precursor polymer is soluble and the material can be readily cast as a film. Subsequently, the precursor film is thermally converted to the final conjugated PPV product. The earliest precursor route to PPV is known as the Wessling precursor route and involves a sulfonium precursor (also referred to as the sulfonium precursor route (SPR)). Other routes can be used to prepare PPV and PPV derivatives. These include the xanthate precursor route (XPR) and the chlorine precursor route (CPR). ... 

Figure 3. Synthesis of poly(phenoxy phenylene vinylene) via the chlorine precursor route...

The XPR has been used to synthesize poIy(2,5 dimethoxy p-phenylene vinylene)(DM-PPV) and the reaction is the same as shown in Figure 2 except that methoxy substituents are present at the 2 and 5 positions of the phenylene ring. The chlorine precursor route (CPR) is used to prepare poly(phenoxy phenylene vinylene) (PO-PPV) and the reaction is shown in Figures. ... 

Poly(phenoxy phenylene vinylene)(PO-PPV) is synthesized via the chlorine precursor route as shown in Figure 3. The CPR is preferred for preparation of precursor polymers with large substituents such as phenoxy. The precursor film is quite flexible and dynamic infrared linear dichroism (DIRLD) studies (stretching the polymer while recording the dynamic infrared spectra) are in progress. 

The infrared spectrum of the PO-PPV precursor film was also monitored during conversion. Only minor changes are observed in the infrared spectra of the film during conversion in the heated transmission cell. This is because the primary change is the loss of HCl and an increase in the vinylene C-H due to increased conjugation in the product. Comparisons are being drawn between PO-PPV and other derivatives synthesized via the chlorine precursor route. A complete characterization of the infrared vibrational modes using both DIRLD and computational calculations in PO-PPV will be made. ... 

B. R. Hsieh, H. Antoniadis, D. C. Bland, and W. A. Feld. Chlorine precursor route to poly(p-phenylene vinylene)-based light emitting diodes, Adv. Mater. 7 36 (1995). 

Of course, the brute force method of reacting silica with ammonia or N2/H2 gases at temperatures in excess of 1,200°C will also yield crystalline sihcon nitride ceramics. Another route that does not involve chlorinated precursors consists of sintering a polymeric precursor such as poly[(methylvinyl)silazane]— [(CH3SiHNH)os(CH3SiCH = CH2NH)o.2] . 

In the case of phenazine, substitution in the hetero ring is clearly not possible without complete disruption of the aromatic character of the molecule. Like pyrazine and quinoxa-line, phenazine is very resistant towards the usual electrophilic reagents employed in aromatic substitution reactions and substituted phenazines are generally prepared by a modification of one of the synthetic routes employed in their construction from monocyclic precursors. However, a limited range of substitution reactions has been reported. Thus, phenazine has been chlorinated in acid solution with molecular chlorine to yield the 1-chloro, 1,4-dichloro, 1,4,6-trichloro and 1,4,6,9-tetrachloro derivatives, whose gross structures have been proven by independent synthesis (53G327). 

The pyrimidine synthesis was therefore changed to the alkynyl ketone route as the appropriate precursors could be formed under much milder conditions. Thus, treatment of the chloro aldehyde 1002 with ethynyl Grignards or lithium species at low temperature, followed by mild oxidation with manganese dioxide, gave the desired chloro alkynyl ketones 1003, which could be successfully converted to the pyrimidine products 1004, by condensation with substituted guanidines, without displacement of the chlorine atom <2003X9001, 2005BMC5346>. 

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