Chlorine precursors

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. 

The generation of PPV and corresponding derivatives via the dihalide approach is possible not only in solution reaction, but also - via the gas phase -in a so-called chemical vapor deposition (CVD) process. In this process, the vapor of a dichlorinated para-xylene (a,a or a,a) is pyrolyzed at moderately low pressures (0,1-0,2 torr) to form a chlorinated para-xylylene intermediate, which then condenses and polymerizes on a suitable, cooled substrate. The coating of the chlorinated precursor polymer can be heated to eliminate HCl, to form PPV 60 (or a PPV derivative) [88]... 

Syntheses of Chlorinated Precursors upon Reaction of N3P3C16 with Natural... 

Fig. 30 Light output for single layer PPV device (obtained from chlorinated precursor), Thickness of PPV film = 700°A7 ...

Regarding the preparation of praseodymia and teibia supported metal catalysts, the information available is rather scarce. All the reported studies have dealt with dispersed noble metal samples. Though metal vapor deposition has been applied in some cases (231), the impregnation techniques have coirstituted the most usual preparation procedure. Chlorine-containing (53,82,85,127,175,278), and chlorine-free (53,84,232,278) metal precursors have been used. As already reported, PrOCl and Tb(3CI have been identified in praseodymia and terbia supported catalysts prepared from chlorinated precursors (82). Water (82,85,127,175), and non-aqueous solvents. 

Chang S., Tanaka P., McDonald-Buller E., and Allan D. T. (2001) Emission Inventory for Atomic Chlorine Precursors in Southeast Texas. Technical Report, University of Texas. 

The silanorbomenes 1, 2, and 3 can be synthesized according to the literature [1, 2]. Hydrogen chloride cleavage of 3 leads to the silicon chlorinated precursor of 13, which is obtained by a Grignard reaction with naphthyl magnesium bromide in high yield (86 %). Similarly, 15 is available from HCl cleavage of 1 and reaction of the latter with fluorenyl lithium. The silicon-chlorinated silacyclobutanes 7, 8, and 11 are synthesized by [2+2]-cycloaddition of dichloroneopentylsilene with isoprene and dimethylbutadiene, respectively [3],... 

The evolution of the mass spectra of the ion-molecule reaction products of m/z 77 ions with ammonia as a function of the nature of the precursor halobenzene is also of interest. The m/z 94 m/z 93 branching ratio measured as 22 78 for the chlorinated precursor becomes 30 70 for the brominated precursor and 49 51 for the iodinated precursor. Moreover, this ratio is still significantly modified (60 40) if ionized iodobenzene is prepared by charge exchange with methylene chloride in the Cl source. The degree of fragmentation of the m/z 94 ions thus appears extremely dependent on the distribution energies of the precursor m/z 77 ions, but the occurrence of isomeric species of the phenyl cation cannot also be ruled out completely. 

Chlorine atoms in Cl3P=N-P(0)Cl2 can be easily replaced by nucleophilic substitution with RONa, yielding compounds (R0)3P=N-P(0)(0R)2 (R = i-propyl, allyl, benzyl and furfuryl). The biological properties of these compounds have been investigated and compared with those of their chlorine precursor. The preparation of the linear thiazylphosphazenes (R0)3P=N-S(02)0R and (R0)3P=N-S(02)-N=P(0R)3 has been described ... 

For the synthesis of dichloro and polychlorophenols the chlorination of a less chlorinated precursor has been the method of choice, doubtless because the presence of one or two chlorine atoms partially deactivates the ring. The preparations of some compounds in this class are listed in Table 8.2 (refs.14-17). 

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. ... 

Tin containing perovskites ASnOs (A = Ca, Sr, Ba) are prepared by a soL gel method starting from tin oxygenated precursor (SnO) or from chlorinated precursors (SnCU). The respective reactivity tests in oxidative coupling show that perovskites prepared from chlorinated precursors have a mudi higher C2 hydrocarbons selectivity than that obtained from oxygenated ones (70% compared to 40% for BaSnOs). This difference in reactivity is interpreted by the modification of the basicity of the system by bulk or surface chlorine (CO2 thermodesorption). 

The sol-gel method has b n used to prepare the ASnOs perovskites as well from the oxygenated (I) as from the chlorinated precursors (II). The preparations are very similar for Ca, Sr and Ba catalysts and are summarized in Scheme I. 

Scheme 1. Summarized ASnOs perovskite preparation (A Ca,Sr3a) by sol-gel method. (I) Oxygenated precursor H) Chlorinated precursors.

The BaSn03 catalysts prepared from oxide or chlorinated precursors (SnCli) have both been studied by XPS after their formation. The position of the peaks in the Ois, Cis, Basd, Sn3d are given in Table 3. 

The second important point is that 10 times more CO2 is adsorbed on BaSnOs (I) than on BaSnOs (ID. This is in agreement with the results of the literature (5,9,10) on other catalysts. It must be noted that this difference is much higher than the change of the specific surface area and can therefore not be directly attributed to it. The shape of TPD curves after CO2 adsorption, on the perovskites treated at 20 C show also dear differences between the catalysts obtained through oxygenated or chlorinated precursors. 

Figure 5 TPD after CO2 adsorption on BaSnOs (I) oxygenated precursors (II) chlorinated precursors.

The results obtained in the present work permit to propose that the selectivity value obtained by preparing the catalysts from chlorinated precursors can qualitatively be relat to the TPD aft CO2 adsorption. CO2 which is a poison for oxidative coupling is less adsorbed on the catalyst prepared from chlorine containing precursors. Thus chlorine is proposed to stabilize the sites which are active in oxidative methane coupling vdth respect to the poisoning by CO2. 

The metal loading on the catalyst was checked by elemental analysis (AES - ICP) and also the residual chlorine atoms, coming from the chlorinated precursors, were detected by ionic chromatography. 

This result has a fundamental importance in the preparation of supported catalysts from chlorinated precursors, which are commonly used due for a low price and an easy solubility in water by means of ultrasound, it is possible to prepare supported catalysts from chlorinated precursors without leaving chlorine atoms, which are able to change the properties of the catalysts, increasing the support acidity or poisoning the metal center. 

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