IL31794A - Process for the manufacture of bipyridyls - Google Patents

Description

PROCESS FOR THE MANUFACTURE OF BIPYRIDYLS MB 00900: 21009; 2150 ; 0150!): 2l!=i66t 21620 This invention relates to yyrid-iae derivatives Bad their maaafaoture and particularl to novol subetitutod pyridinoo nd pgoooBoos·' -for—-he—toaBufacture-of■ ■su-bs4i-tutod pyridinoo, and to a process for the manufacture of bipyridyls from substituted pyridines.

According to the present invention we provide a process for the manufacture of bipyridyls which comprises reacting the corresponding substituted pyridine with ammonia in the vapour phase, the substituted pyridine being a 2-(pyridyl)-tetrahydro-pyran or tetrahydrothiopyran, a 4-(pyridyl)-tetrahydropyran or -tetrahydrothiopyran or a substituted pyridine wherein the substituent is a group of the structural formula wherein R represents a hydrogen atom, a halogen atom, a hydroxy group, an alkoxy group or an amino group, and R^ and Rg each wherein X represents an atom of oxygen or sulphur, n is 0, 1 or 2 and m is 1 and each represents a hydrogen atom or an alkyl, ■I' lcfn^ aryl, alkaryl >r "cyclo 'al piiatdiO group.

In the pyridine derivatives (including the pyridyl tetrahydro-pyrans and tetra ydrothiopyrans), the substituent may be in the 2, 3 or 4 position in the pyridine nucleus.

The reaction is preferably carried out in the presence of molecular oxygen.

The substituted pyridine starting material in the vapour phase is heated with ammonia advantageously at a temperature in excess of 250°C, preferably 350-450°C, for example about 380°C, usually in the presence of catalyst. Suitable catalysts include alumina, silica, silica-alumina, magnesia, chromia and mixtures thereof; these catalysts may contain platinum and/or palladium (as the metal or its oxide) in inely-divided form. Particularly suitable catalysts are the dehydrogenation catalysts, e.g. nickel, cobalt, copper, chromium and copper chromite. Preferably the reaction mixture contains molecular oxygen as, for example, oxygen gas which can be conveniently added in the form of air, although any molecular oxygen containing gas may be used.

The starting material can be vaporised simply by heating it to the required temperature and a particularly suitable technique is to drop the material in a stream of droplets onto a hot surface, for example onto a vaporiser or onto the catalyst for the reaction with ammonia. The material can be conveniently vaporised in a vaporiser prior to contact with the catalyst. Some of the starting materials are, however, tacky, viscous liquids or solids at ordinary temperatures and these are conveniently dissolved in a suitable solvent prior to vaporisation. Examples of suitable 31794/2 solvents for this purpose are water and alcohols, especially lower aliphatic alcohols and particularly methanol.

The bipyridyls produced by the process can be isolated from the reaction products by known techniques. For example, the gaseous reaction products can be condensed and the bipyridyl can then be isolated from the condensate by solvent extraction and/ or fractional distillation, if desired under reduced pressure. If water is present in the reaction product obtained in the production of 4, 4' -bipyridyls, these bipyridyls can be separated by filtration.

The process, whether a single or two-stage process, can be carried out batch-wise but has the advantage that it can be carried out as a continuous operation.

The process is particularly suitable for the production of 4, 4' -bipyridyls although other isomers, for example 2, 2·-, 2, 4'- , 2, 3'- and 3, 4'- bipyridyls can be obtained by suitable choise of the Starting material.

' Pyridyl tetrahydropyrans and pyridyl tetrahydrothiopyrans are converted by the process of the invention into the corresponding bipyridyl by replacement of the oxygen (or sulphur) atom of the tetra-hydro(tMo) ^yranjd nucleus by a nitrogen atom and simultaneous dehydro genaticn to form a pyridyl nuclsus. Thus for example, a 2-(4-pyridyU-tetrahydrbpyran will yield a 2, 4J -bipyridyl and a 4-(4-pyridyl)-tetra-hydro pyran will yield a 4, 4' -bipyridyl. Substituted pyridines wherein the substituent is -c(R) (R^) (Rg) are converted to bipyridyls in a similar manner. but in this case replacement of two groups -OR by a nitrogen atom is accompanied by ring closure to form a pyridyl nucleus. The simplest compounds wherein the substituent is *e(R) ( ^) (Rg) are ( pyridyl) -alkane diols, especially 3-(pyridyl)-pentane-l, 5-diols, i. e. where R is hydrogen and Rg and Rg each is -CHgCHgOH, Formation of a bipyridyl from these compounds is the result of replacement of the two -OH groups (eliminated as H^O) by a nitrogen atom with simultaneous ring closure and dehydrogenatlon to form a 31794/2 pyridyl nucleus. Thus a 3^(2 -pyridyl) -pentane-l, 5-diol will yield '-bipyridyl, e. * ; g and included for use i the present invention are compounds having this basic formula but containing one or more substitutentsi for ex- ample alkyl or alkoxy groups in either or both of the pyridyl or tetra - hydropyranyl nuclei.

Unsubstituted 2 ^(pyridyDtetrahydropyrans have the structural formula: and other compounds for use in the invention are those wherein either or both of the heterocyclic nuclei are substituted. 31794/2 for example by alkyl or alkoxy groups, especially compounds of formula wherein R^ represents an alkyl group, an alkoxy group, a heterocyclic group containing a N-heteroatom (which is linked to the carbon atom of the tetrahydropyranyl group) which may also contain one or more other heteroatoms for example a «N group or a dialkylamine group^ for example a -N(CHg)g group* ! The other hovel substituted pyridines which may be used in the invention have the basic structural formula including compounds having this basic formula but which contain one or more substituents, for example alkyl groups on one or more of the other carbon atoms of the pyridine nucleus. Also included are compounds of the above basic formula but having a substituent on the nitrogen atom, for example substituted pyridine N -oxides. 4-(pyridyl)-tetrahydropyrans or -tetrahydrothiopyrans, can be made by reacting a 2,-haloethyl-r3«(pyridyl)-propylether or thioether respectively with an active alkali metal compound.

The reagents are preferably reacted in equimolar proportions and preferably at a temperature in the range -10°C to -80°C in solution in a mddium containing liquid 31794/2 Φ ammonia. However, the reaction may be carried out in the absence of a solvent or in solvents other than liquid ammonia, for example hydrocarbons and ethers, in which case higher temperatures, e. g. up to 40°C, may be employed. Higher temperatures can also be achieved by carrying out the reaction under superatmospheric pressure. The preferred active alkali metal compounds are alkali metal amides, especially sodamide.

The 4-(pyridyl)-tetrahydropyran or -tetrahydro-thiopyran, may be isolated from the reaction mixture by conventional techniques, for example by decomposing any excess metal amide by addition of an ammonium salt; extraction of the resulting product with an organic solvent which is liquid at ordinary temperatures e. g. ether; washing the organic layer with water and separating the organic solvent and the product by distillation.

The 2»-haloethyl 3-(pyridyl)propyl ethers and thioethers have the general structural formula - where A Is O or S, and Hal represents a halogen atom. 2,-haloethyl 3-(pyridyl)propyl ethers or thioethers can be produced by interacting an alkali metal derivative of a picoline with a di-(2-haloethyl)ether or thioether.

The alkali metal derivative of the picoline may be made by Interaction of the picoline with an active alkali metal compound e.g. an alkali metal amide (produced for example by dissolving an alkali metal in liquid ammonia in the presence of ferric ions) or an alkyl derivative of an alkali metal e.g. a lithium alkyl. The preferred nethod of making the alkali metal derivative of the picoline comprises interaction of equimolar proportions of sodamide or potassanide with the picoline which, if the 4-pyridyl derivative is required is a 4-(or gamma)-picoline, at a temperature in the range -40°C to -80°C in solution in a medium containing liquid ammonia. The reaction nay be carried out under pressure to enable temperatures above -30°C to be employed.

The alkali metal derivative of the picoline may be reacted with the di-(2-haloethyl)ether, thioother ov- amino by addition of the former to the latter and ensuring a stoichiometric excess of the latter throughout the reaction. The addition nay conveniently be carried out at a temperature of from -10°C to -80°C preferably using equimolar proportions of the reagents. However, temperatures of up to 40°C may be employed, if necessary by carrying out the reaction under increased pressure. The reaction may conveniently be carried out in solution, for example in a solvent comprising or containing liquid ammonia.

The di-(2-haloethyl)ether,? thioether jre-ataine is preferably a di-(2-chloroethyl)ether, /thioether 2-(pyridyl)-tetrahydrop3Tans or tetrahydrothiopyrans can be prepared by the reaction of the appropriate pyridyl lithium or pyridyl Grignard reagent with a 2-halotetrahydropyran or tetra-hydrothiopyran. The pyridyl group becomes attached to the tetrahydropyranyl group by the carbon atom which carried the lithium atom or the Grignard reagent radical. 2-pyridyl lithium can be prepared by reacting 2-chloro-, or preferably 2-bromo- pyridine with n-butyl lithiun at low temperatures, for example below 0°C and preferably about -40° C or lower. 4-pyridyl lithiun can similarly be prepared from 4-bromo- or 4-chloro-pyridine. 2-pyridyl Grignard reagents are easily prepared by reacting 2-bromo-pyridine with e.g. magnesium in the presence of an alkyl halide, e.g. an alkyl bromide by the ' antrainment 1 procedure of Overhoff and Proost (Rec. Trav. Chin.21, 179, (1938). 4-pyridyl Grignard reagents can similarly be prepared from 4-bromo yridine. In each case the reagents need simply be mixed but if desired an inert organic solvent may be employed. Any inert solvent may be used, for example aliphatic or aromatic hydrocarbons, ethers and ketones, but in view of the low temperatures employed the solvent preferably has a freezing point of below -50° C.

The pyridyl and/or the tetrahydro yranyl or tetrahydrothio-pyranyl nuclei may be substituted and examples of substituents which may bo present are halogen atoms, alkyl groups and alkoxy groups, and the tetrahydropyran or tetrahydrothiopyran may also carry a heterocyclic substituent. In particular, the totrahydro-pyran may have the formula Z where Y represents a chlorine atom or a bromine atom, Z represents a halogen atom or a hydrogen atom, and B represents a hydrogen atom, an alkyl or alkoxy group (especially a methoxy group), a heterocyclic group e.g. of formula 0, or an amine group e.g. -N(CH,)p. The stereochemistry of the tetra- hydropyranyl is not important.

The reaction between the pyridyl lithium or pyridyl Grignard reagent and the 2-halo-tetrahydropyran or tetrahydrothiopyran con be effected sinply by nixing the reagents but if desired either or both of the reagonts nay be enployed in the fona of a solution* It is an advantage that the reagents do not require to be separated from the reaction mixture in which they have been prepared and thus if they are prepared in solution it is sufficient sinply to nix the resulting solutions. The temperature will usually be maintained below 0°C and preferably about -40°C or below since the reagents tend to be unstable at ordinary temperatures.

The 2-pyridyl tetrahydropyrans or totrahydrothiopyrans wherein B of the tetrahydrothiopyranyl residue (see above) is a hydrogen atom can bo separated from the reaction mixture in which they have been prepared by allowing the nixture to warn to room temperature, acidifying it for example by adding hydrochloric acid, and separating the resulting organic and aqueous phases. The organic phase is then neutralised and extracted with ether, and the extract fractionally distilled to recover the fairly pure product which can bo purified by further fractional distillation.

The product wherein B of the tetrahydrothiopyranyl residue (see above) is other than a hydrogen atom can be separated by adding an ammonium salt of an acid and then separating the resulting phases, extracting with ether and distilling as above. The ammonium salt, for example ammonium chloride, is preferably used in the form of a solution which advantageously can be an aqueous solution . 31794/2 Substituted pyridines wherein the eubstituent has the structural formula -CfRKRjMRg) can be prepared by reacting the appropriate pyridine derivative with a metal amide or an organo-lithium compound and with an appropriate halogenated organic compound or (if a group -CHg. CftgOH, -CHg. CHgSH is to be introduced) with an alkylene-oxide or -sulphide.

Pyridyl alkane diols or pyridyl alkane dithiols can be prepared by reacting an alkyl pyridine with a metal amide or an organolithiu s compound and with an alkylene oxide or alkylene sulphide respectively. This process is especially suitable for the production of 3-(4,-pyridyD-pentane-1, 5-diol or 3-(4,ppyridyl)-pentane-l, 5-dithiol by reacting gamma- picoline with a metal amide or an organoUthlum compound and with ethylene oxide or ethylene sulphide respectively.

The reaction can if desired be carried out simply by mixing the reagents in appropriate amounts in the absence of a solvent, but usually It is carried out in a solvent for the pyridine derivative. Any solvent may be employed which is inert to the reactants and to the reaction product. Alternatively an excess of the alkyl pyridine or alkanolpyridine or of pyridine itself may be provided to act as a solvent. A particularly suitable solvent for use in reactions involving a metal amide is liquid ammonia although others, for example organic amines such as diethylamine may be used.

Examples of solvents which may be used when an organoUthlum comound is employed are hydrocarbons. especially aliphatic ethers, and particularly diethyl ether, and dimethyl sulphoxide, especially a solution of the sodium salt of dimethyl sulphoxide in excess dimethyl sulphoxide,, The temperature at which the reaction is carried out is to some extent dependent upon the particular solvent employed and the pressure at which the reaction is effected. Thus when liquid ammonia is employed as the solvent at ordinary pressure, the temperature should be -33°C or below but temperatures above this, for example up to room temperature may be employed using an amine or an ether as the solvent* Usually, however, the reaction is carried out at a temperature below 40°C.

Temperatures higher than those mentioned above may be used, and these can be achieved by carrying out the reaction under superatmospheric pressure, for example in an autoclave.

The metal amide may be in particular an alkali metal amide, particularly sodamide or potassamide. The amide may be added as the pre-fortied oompound or it may be formed in situ. For example sodamide or potassamide can bo formed in situ by adding metallic sodium or potassium to anhydrous liquid ammonia in the presence of a oatalyst, for example ferric nitrate (ferric ions). The organolithium compound may be in particular a lithium alkyl,for example lithium et¾i or lithium butyl, or a lithium phenyl or lithium benzyl. wherein the substituents As stated hereinbefore the -aew compounds /of tho-invontion the formula C(R) (Rj) (R2) / can be prepared from a pyridine derivative and the appropriate halogenated organic compound. Pyridine derivatives which may be used include those of formula 31794/2 wherein R, R ^ and Rg are as hereinbefore defined.

The halogenated organic compounds which can be reacted with the pyridine derivative have the formual P Hal wherein p represents R j or Rg, as hereinbefore defined, and Hal is a halogen atom, especially a chlorine atome. The product obtained by reacting pyridine derivative (a) with halogenated organic: compound D Hal can have the formula depending upon whether one mole or two moles of D Hal are employed per mole of the pyridine derivative.

The pyridine: derivatives (b) and (c) (prepared for example as described in the immediately preceding paragraph)- can be reacted with the organic compound D Hal to form the compound (d). Alternatively the compounds (d) can be prepared by reacting pyridine derivatives (b) with a metal amide or an organolithium compound and an alkylene oxide or alkylene sulphide, particularly an ethylene compound. The use- of alkylene compounds having 3 or more carbon atoms has the advantage that the aliphatic group ihtroduced into the pyridine nucleus nay have an alkyl group as substituent; bipyridyls wherein the pyridine nuclei carry alkyl substituents can be obtained from these derivatives.

A particular pyridine derivative which can be used is 1-( '-pyridyl)-n-propan3-ol or -thiol which can be produced by reacting gamiaa picoline with a metal amide and with ethylene oxide or ethylene sulphide in amounts such that the mole ratio of metal amide:gamma picoline is about 1:1 and of ethylene compound: gamma picoline is also about 1:1.

The products can be separated from the reaction mixture in which they are formed in any convenient manner. For example, especially if the compound has been prepared in liquid ammonia, ammonium chloride can be added and the ammonia (or other solvent) removed by evaporation. The amount of ammonium chloride is usually at least 1nr>le per mole of product to be separated. The residue is extracted with a solvent, for example pyridine, methylene chloride or diethyl ether which is then allowed to evaporate. The reaction product is then isolated from the residue by fractional distillation under reduced pressure. In the case or where pyridyl alkane diols, /dithiols or diaa-inoo are prepared from gamma picoline and an alkylene oxide° /sulphide .or imi-no respectively, the amounts of the metal amide or organolithium compound and of the allcylene derivative used are preferably at least 2 moles of the alkylene derivative and at least 2 moles of the metal amide or organolithium compound per mole of the alkylpyridine. It is especially preferred that the amounts of both the allcylene derivative and the metal amide or organolithium compound are slightly above 2 moles per mole of the alkyl pyridine. The metal amide or the organolithium compound can be added before the alkylene 31794/2 derivative or the three reagents can be mixed together initially.

Pyridyl tetrahydropyrans or tetrahydrothio-pyrans can also be prepared by heating the appropriate pyridyl alkane diol or dithiol at a temperature of at least 250°C, preferably in the presence of a catalyst. Pyridyl tetrahydrothiopyrans can also be prepared by heating the appropriate pyridyl alkane diol in the presence of hydrogen sulphide, or by heating a pyridyl alkane (hydroxyl thiol) in the presence or absence of hydrogen sulphide.

The simplest pyridyl alkane diol and tcSthiol which may be used are 3-(pyridyl)<-pentane-l, 5-diol or dithiol. The diol or dithiol may be employed without isolation from the mixture in which it has beeia repared . The temperature at which the diol or dithiol is heated to convert it to the corresponding pyridyl cyclic ether or pyridyl cyclic thioether is at least 250°C, and preferably is at least 300°C. We especially prefer to employ a temperature of the order of 380°C. It is sufficient simply to heat the diol or dithiol at the desired temperature, but we prefer to carry out the heating in the presence of a dehydration catalyst, for example alumina, silica, silica/alumina or mixtures thereof. A particularly convenient technique is to pass the diol or dithiol in vapour phase through a bed of the catalyst contained in a tube , for example a glass tube. If desired the heating may be carried out under super-atmospheric pressure, in which case lower temperatures may be needed to effect the conversion.

The invention is illustrated but in no way limited by the following examples: - Exam les L_ to 42_ These examples illustrate the conversion of substituted pyridines into bipyridyls.

The experimental procedure in each example was as follows: A catalyst bed was prepared from a pelleted form of the catalyst (see below) to the specified depth in a vertical glass reactor tube of internal diameter ί inch. The tube was fitted with a central thermocouple pocket and contained Raschig rings above the catalyst bed. The Raschig rings did not completely fill the tube. The tube was positioned in a vertical furnace maintained at the appropriate temperature.

The substituted pyridine was dissolved in water or methanol or (__Example 32) pyridine and the solution was fed to the top of the reactor tube where it was vaporised on contact with the Raschig rings. The vapours were passed downr wardly through the catalyst bed. The vapours were mixed with oxygen, nitrogen or ammonia as indicated in the Table for passage through the catalyst bed, although in a few cases mixing was carried out below the surface of the catalyst bed.

The reactor effluent was condensed and the condensate if liquid (as in the majority of the experiments) was analysed by gas/liquid chromatography using standard techniques. Where the condensate was a solid this was dissolved in methanol and the solution was analysed.

In the Table the' catalyst is designated by a reference letter A, B, C or D:- A. t" x pelleted alumina (Actal 'Α') B. activated copper oxide/chromia (i.C.I. 26-3) C. 0.5/° platinum on 50 silioa-alumina a bed of a separate bed of D. /l3¾ alumina silica + /alumina (Crosfield - Grade 77) In the Table also: •Bipyridyl1 means 4,4'-bipyridyl unless otherwise stated •Length' is the length of the catalyst bed 'Temp.' is the temperature of the oatalyst bed "dilution* is in terms of gms starting material/mis solvent •MeOH' is methanol 9 11 4-(4-pyridyl)-tetrahydropyran 4-(4-pyridyl)-tetraydropyran 12 i TABLE (continued) - 2§ - 31794/2 In the above Table the product listed is the major reaction product. However* in many examples other products were identified as follows: 1, 6. 7, 8, 9. 4-<4* pyridyl)-tetrahydropyran 21 to 36 17, 18 4-(2-pyridyl)-tetrahydropyran 19, 20 (4-(3-pyridyl)-tetrahydropyran • ■ . ( ( 3' -methyl -3, »-bipvridyl The majority of the products (including those referred to as "other products") were identified by comparison with authentic reference compounds. Those which could not be so identified were subjected to fractional distillation or to gas/ liquid chromatographic analysis and their spectral data is given below: 3, 4,-Blpyridyl I. R. max (liquid film) 3050, 2950, 1600, 1580, 1465, 1420, 1400, 1025, 1015.990, 840, 800, 765 and 715 cm"1 N. M. R. τ (CC14) 1. 28, 1. 50, 1. 69. 2. 26, 2. 66. 2. 76 (Relative intensities 1:2: 1: 1:2:1) M. S. » 156. 0684 <£10ΗβΝ2 has = 156. 0687) The compound gave a bright buttercup yellow colour with zinc dust/ acetic acid. 3 '-Methyl 3. 4'-Bipyridyl I. R. \> max (liquid film) 3050, 2950, 1600, 1530. 1450. 1440, 1400. 1020, 835, 820, 805, 750. 740 and 720 cm"1 N. M. R. I (CCl.) 1. 4-1. 7. 2. «5. 2. 7. 2. 95, 7. 72 4 (Relative intensities 4:1: 1:1:3) 170. 0843 (C has = 170. 0843) 11

Claims (12)

31794/ 3

1. A process for the manufacture of bipyridyls which comprises reacting the corresponding substituted pyridine with ammonia in the vapour phase the reaction being carried out at a temperature in excess o 250°C. in the presence of a catalyst, the substituted pyridine being a 2-(pyridyl)tetrahydropyran or tetrahydrothiopyran, a 4-(pyridyl) tetrahydropyran or tetrahydrothiopyran, or a substituted pyridine wherein the substituent is a group of the structural formula -C(R)(Rj)(RjJ wherein R represents a hydrogen atom, a halogen atom, a hydroxy group, an alkoxy group or an amino group, and R^ and R^ each represents a group of the general formula -CH (XR_)„ CH (XR . )_ n -n rci 3 wherein X represents an atom of sulphur or oxygen, n is O, 1 or 2 and m is 1 or 2, and Rg and R^ each represents a hydrogen atom or an alkyl , alkenyl, aryl, alkaryl, ar alkyl or cyclo- alkyl group.

2. A process as claimed in claim 1 wherein the reaction is carried out in the presence of molecular oxygen.

3. A process as claimed in claim 1 wherein the temperature is from 350°C to 450°C.

4. A process as claimed in any one

5. A process as claimed in any one of claims 1 to 4 wherein the reaction is carried out in the presence of molecular oxygen in the form of oxygen gas.

6. A process as claimed in claim 5 wherein the oxygen gas is added In the form of air.

7. A process as claimed in any one of the preceding claims wherein the substituted pyridine is obtained in the vapour phase by evaporazation of a solution of the derivative.

8. * A process as claimed in claim 7, wherein the solvent comprises water*

9. A process as claimed in claim 7, wherein the solvent is an alcohol. 31794/3

10. A process as claimed in claim 9, wherein the alcohol is methanol.

11. A process as claimed in any one of the preceding claims which is carried out as a continuous operation.

12. A process as claimed in any one of the preceding claims wherein the substituted pyridine starting material is a pyridyl alkane diol. S. HOROWITZ & CO. AGENTS FOR APPLICANTS