Aug.  14,  2008  5  US 2008/0194886 Al  waves and the activated products are removed continuously  from said reactor via an outlet orifice.  [0111]  In the case of actinic heating by microwave, it is  recommended to use a power evolved by the microwaves of  between 1 and 50 watts per milliequivalent of aromatic sub› strate.  It  is also desirable to accept the constraint according to  which the power evolved by the microwaves is between 2 and  100 watts per gram of reaction mixture.  [0112]  The catalyst according to the invention may be used  concomitantly with a catalyst acknowledged as being a  phase-transfer catalyst, especially when this catalyst is a cata› lyst of cationic nature.  [0113]  Such a concomitant use is all the more appropriate  since the mechanism of action appears to be different.  [0114]  The best phase-transfer catalysts that may be used  are generally oniums, ie they are organic cations whose  charge is borne by a metalloid. Among the oniums that may be  mentioned are ammoniums, phosphoniums and sulfoniums.  However, other phase-transfer catalysts may also be used  provided that the phase-transfer catalysts are positively  charged. They may also be cryptand cations, for example  alkali-metal-cryptand crown ethers.  [0115]  These phase-transfer catalysts may be used in the  presence or absence, preferably in the presence, of an alkali  metal cation that is particularly heavy and thus from a high  atomic row, such as cesium and rubidium.  [0116]  When the present invention is used to carry out a  chlorine/fluorine exchange reaction, a dipolar aprotic solvent,  a solid phase consisting at least partially of alkali metal fluo› rides and a reaction-promoting cation are generally used, said  cation being a heavy alkali metal or an organic phase-transfer  agent, this agent being of cationic nature.  [0117]  The content of alkali metal cation, when it is used as  promoter, is advantageously between 1 mo! % and 5 mo! %  and preferably between 2 mo!% and  3  mo!% of the nucleo› philic agent used. These ranges are closed ranges, ie they  include their limits.  [0118]  The reagent may comprise, as promoter, phase› transfer agents that are oniums ( organic cations whose name  ends with onium). The oniums in general represent 1 mo! %  to 10 mo!% and preferably from 2 mo!% to 5 mo!% of the  aromatic substrate, and the counterion may be of any nature  but is usually halogenated.  [0119]  Among the oniums, the preferred reagents are tet› raalkylammoniums of 4 to 28 carbon atoms and preferably  from 4 to 16 carbon atoms. The tetraalkylammonium is gen› erally tetramethylammonium.  [0120]  Phosphoniums and especially phenylphosphoniums  should also be mentioned, which have the advantage of being  stable and relatively sparingly hygroscopic; however, these  reagents are relatively expensive.  [0121]  The aprotic solvent of halex type advantageously  has a significant dipolar moment. Thus, its relative dielectric  constant epsilon is advantageously at least equal to about 1  O;  preferably, the epsilon is less than or equal to 100 and greater  than or equal to 25.  [0122]  It  has been possible to show that the best results  were obtained when dipolar aprotic solvents with a donor  index of between 1.0 and 50 were used, said donor index  being the llH ( enthalpy variation) expressed in kilocalories of  the combination of said dipolar aprotic solvent with antimony  pentachloride.  [0123]  The oniums are chosen from the group of cations  formed by colunms VB and VIB as defined in the Periodic  Table of the Elements published in the supplement to the  Bulletin de la Societe Chimique de France in January 1966,  with four or three hydrocarbon-based chains, respectively.  [0124]  In general, it is known that a fine particle size has an  influence on the kinetics. Thus, it is desirable for said solid in  suspension to have a particle size such that its  d,$_{0 }$ (  defined as  the mesh that allows 90% by mass of the solid to pass through)  is not more than 100  µm,  advantageously not more than 50 µm  and preferably not more than 200 µm. The lower limit is  advantageously characterized in that the d$_{10 }$of said solid in  suspension is not less than 0.1 µm  and preferably not less than  1 µm.  [0125]  In general, the ratio between said nucleophilic  agent, preferably the alkali metal fluoride, and said substrate  is between 1 and 1.5 and preferably in the region of 5/4  relative to the exchange stoichiometry.  [0126]  The mass content of solids present in the reaction  medium is advantageously not less than $^{1}$/s, advantageously  …  and preferably  1 A  [0127]  The stirring is advantageously performed such that  at least 80% and preferably at least 90% of the solids are  maintained in suspension by the stirring.  [0128]  According to the present invention, the reaction is  advantageously performed at a temperature ranging from  about 150 to about 250°  C. In the present description, the term  "about" is used to illustrate the fact that the values that follow  it correspond to mathematic round-ups and especially that, in  the absence of a decimal point, when the figure( s) the furthest  to the right in a number are zeros, these zeros are positional  zeros rather than significant figures, except, of course, if  otherwise specified.  [0129]  However, it should be pointed out that when the  temperature increases, the kinetics increase but the selectivity  decreases.  [0130]  Another aim of the present invention is to provide a  composition capable of serving as a reagent for nucleophilic  substitution, especially aromatic nucleophilic substitution.  [0131]  This aim is achieved by means of a composition  comprising:  [0132]  a polar aprotic solvent;  [0133]  a nucleophile;  [0134]  a compound of formula  (I).  [0135]  It  should be noted that the compounds of formulae  (I)  and (II) are particularly suitable for the usual recycling  techniques.  [0136]  Another aim of the invention is to provide, besides  that of having provided a novel family of novel compounds  that is useful as nucleophilic substitution catalysts having a  pronounced catalytic nature.  [0137]  Another aim of the present invention is to provide a  process for synthesizing compounds that are used or that may  be used as catalysts for second order nucleophilic substitution  and especially for SN  Ar  nucleophilic substitution.  [0138]  These aims have been achieved with compounds of  formula  (I)  in which the number of alkyl substituents is not  more than 2 and in which the total number of carbons is not  less than 14 and preferably 16 per positive charge borne by the  molecule.  It  should also be pointed out that it is particularly  advantageous to have molecules that are not completely sym› metrical around one of the atoms  Z, but also around one of the  atoms Pn.  [0139]  Thus, it may be indicated that the sum of the carbons  in the radicals  R$_{1}$ ,  R$_{2}$ ,  R$_{3}$ ,  R$_{4}$ ,  Rs and R$_{6 }$ is greater than 12,  preferably not less than 14 and advantageously not less than  16.  [0140]  The condition regarding the alkyls may also be  expressed by indicating that not more than 2 and preferably  not more than one of the radicals  R$_{1}$ ,  R$_{2 }$ and R$_{3}$ ,  on the one  hand, and/or  R$_{4}$ ,  Rs and R$_{6}$ ,  on the other hand, represent an  alkyl group. 