text: as used herein the term selectivity means the weight of the particular product divided by the total weight all products in the product stream . u . s . pat . no . 5 , 449 , 780 to kosak ( kosak ) taught a batch process for hydrogenating 2 - methylglutaronitrile to 1 , 3 and 1 , 5 - dialkylpiperidone - 2 . in the process of this patent , a mixture of the reactants , 2 - methylglutaronitrile , water , an alkylamine and a hydrogenation catalyst , is charged into a reactor . the reactor is then purged and pressurized with hydrogen , and heated to the proper conditions for reaction . it is known that under the reaction conditions of kosak that the liquid reactants , as well as the dissolved byproduct ammonia , remain in substantially two separate phases throughout the majority reaction process . the 2 - methylglutaronitrile has only limited solubility in the aqueous amine solution and the concentration of the amine is predominately distributed in the water phase . thus , in the kosak reaction system , there are present the solid catalyst phase , the gas phase and two liquid phases . the kosak process also has a high selectivity to the formation of high boiler byproducts , particularly towards the formation of bis - 1 , 5 -( alkylamido )- 3 - methylpentane . in the reaction of methylamine with 2 - methylglutaronitrile , the selectivity of the kosak process to bis - 1 , 5 -( methylamido )- 3 - methylpentane ranges from 12 to 40 %. during the refining process , this byproduct ( and when the synthesis is carried out with amines higher than methylamine , corresponding higher alkyl byproducts of this analogous structure ) causes serious problems in producing a purified product . under the distillation conditions the byproduct bis - 1 , 5 -( methylamido )- 3 - methylpentane ( and corresponding higher alkyl compounds formed in the synthesis of the 1 - alkyl - 3 - methylpiperdone - 2 or 1 - alkyl - 5 - methylpiperdone - 2 according to kosak ) is cyclized according to the reaction shown below : ## str1 ## in the continuous , single liquid phase process of the present invention , the continuous removal of product combined with the continuous feed of the reactants , according to fig1 allows the reaction to take place in one single liquid phase and results in a low selectivity towards high boiling by products , particularly bis - 1 , 5 -( alkylamido )- 3 - methylpentane . this single phase reaction seems to be more favorable with respect to equilibrium and kinetic considerations than the teachings of the prior art . the single liquid phase reaction of the present invention is achieved by the addition of a homogenizing solvent to the mixture of the reactants and the catalyst . throughout the reaction , the present process continues to maintain the concentrations of the water solution of the alkylamine , the homogenizing solvent , and 2 - methylglutaronitrile ( as weight percents of the total weight of the liquid phase reaction mixture ) within the single phase region -- that is that region bounded by the lines connecting points a , b , and c of fig1 . the homogenizing solvent may be any solvent , non - reactive in the reaction environment , which is miscible with water and in which the alkylamine and 2 - methylglutaronitrile are soluble to the limits required in fig1 . preferred solvents are dioxane , n - methylpyrrolidone , 1 - alkyl - 3 - methylpiperidone - 2 or 1 - alkyl - 5 - methylpiperidone - 2or a mixture of 1 - alkyl - 3 - methylpiperidone - 2 and 1 - alkyl - 5 - methylpiperidone - 2 or other n - methyl or higher n - alkyl lactams that posses the required properties of water miscibility and solubility for the alkylamine and 2 - methylglutaronitrile . in particular , a mixture of 1 , 3 and 1 , 5 - dimethylpiperidone - 2 , or n - methylpyrrolidone is preferred as the homogenizing solvent . in the present process a homogenizing solvent in which the product 1 - alkyl - 3 - methylpiperidone - 2 and 1 - alkyl - 5 - methylpiperidone - 2 is soluble is preferred , but not required so long as the product 1 - alkyl - 3 - methylpiperidone - 2 and 1 - alkyl - 5 - methylpiperidone - 2 can be drawn off as a continuous , homogeneous product stream . in the continuous process , the concentration limits of fig1 may be met by adjusting the ratios of the reactant feed ( the water solution of the alkylamine and 2 - methylglutaronitrile ) and the product take - off to be within the region of a single phase mixture as defined in fig1 . for example according to the present process as shown in fig1 when the concentration of 2 - methylglutaronitrile is 25 % by weight then the concentrations of the water solution of the alkylamine must be 40 % by weight and the concentration of the homogenizing solvent must be 35 % by weight . fig1 also indicates that at very low concentrations of 2 - methylglutaronitrile or at very high concentrations of water the concentration of the homogenizing solvent may be zero . the concentration of the primary alkylamine in the water solution may be any concentration of the alkylamine which is fully water soluble at the reaction conditions . this value will vary with the particular alkylamine used as a reactant . generally for methylamine , the concentration is preferred to be 40 % by weight , which is approximately the solubility of methylamine in water at room temperature and normal air pressure , but the concentration may be lower or slightly higher as conditions of temperature and pressure permit . the presence of the homogenizing solvent in the reaction mixture provides more advantages than simply the conversion of a heretofore known batch process to a continuous process . the inventor has also found that by including the homogenizing solvent , the hydrogenation reaction proceeds at a slightly faster rate and with a surprising increase in 1 , 3 and 1 , 5 - alkylmethylpiperidone - 2 selectivity and a decrease in the formation of high boiling byproducts particularity bis - 1 , 5 -( alkylamido )- 3 - methylpentane . the present invention allows for a more favorable mix of products than is taught in the prior art . the favorable selectivity of the present invention is independent of the process being run as a batch or a continuous process . this selectivity is also independent of the type of continuous reactor which is used to run the present process . conventional commercial hydrogenation catalyst are useful in the process of the present invention . such catalysts are group viii metals supported on substrates such as graphite , carbon , alumina , strontium or calcium carbonate , silicas , kieselgur , titania or zirconia . palladium is the preferred group viii metal catalyst . the amount of catalyst employed will vary with the particular catalytic metal employed , the concentration of the metal on the substrate , the type of reactor and the reaction conditions . a promoter such as platinum , rhenium , tin , and ruthenium or combinations thereof may be used with the catalyst . the concentration of the promoter may be from about 0 . 5 % to about 5 % by weight of the metal on the catalyst . it is preferred to carry out the process at temperatures above about 150 ° c . and at a pressure above about 27 bars ( 400 psi ). hydrogen should be present in the reactor in at least the stoichiometric amount . by stoichiometric is meant that the amount of hydrogen present is at least that amount sufficient to convert the nitrile to alkylamines and ammonia . a continuous process according to the present invention may be run in continuous fixed bed reactor , a continuous stirred tank reactor , in a bubble column or an external loop reactor . this example shows a continuous fixed bed hydrogenation of 2 - methylglutaronitrile to 1 , 3 and 1 , 5 - dimethylpiperidone - 2 according to the present invention . 18 . 3 grams ( 60 cc ) of 4 × 6 mash granular 2 % by weight palladium on carbon hydrogenation catalyst was charged into a 36 inch ( 91 . 4 cm )× 0 . 75 inch ( 1 . 9 cm ) diameter hastelloy c oil - jacketed , trickle bed reactor designed for continuous operation . the hydrogenated product recycle stream ( product 1 , 3 and 1 , 5 - dimethylpiperidone - 2 , other organics , a water solution of a primary alkylamine and amine ) was used as the solvent diluent for this process . an aqueous methylamine solution , 40 % amine by weight , was initially recycled over the hydrogenation catalyst at a rate of 100 ml per hour at 180 ° c . and 34 bars of hydrogen pressure . two streams were co - fed into the reactor . one stream was 2 - methylglutaronitrile ( 99 . 5 % by weight available from e . i . dupont de nemours and company , inc . wilmington , del . ); the other was 40 % by weight aqueous solution of methylamine . the feed rate was 7 . 4 ml / hr for the 2 - methylglutaronitrile and 8 . 2 ml / hr for the aqueous amine . the recycle ratio was 6 . 4 to 1 . the hydrogen flow rate used was 498 cc / min . the concentrations of a water solution of a primary alkylamine , 2 - methylglutaronitrile and the 1 , 3 and 1 , 5 - dimethylpiperidone - 2 homogenizing solvent fell within the weight percents required by fig1 . a product stream was removed at a rate of 15 . cc / min from the reactor mixture and sent to a 2 liter stainless steel separator and held at 0 . 34 bar ( 5 psi ) to allow the separation of hydrogen and ammonia from the product . hydrogen and ammonia that separated from the product were vented to a nitrogen exit purge stream . the product take - off and reactant feed rates were such that the concentrations of a water solution of a primary alkylamine , 2 - methylglutaronitrile and the 1 , 3 and 1 , 5 - dimethylpiperidone - 2 homogenizing solvent continued to fall within the weight percents required by fig1 . after 45 hours of continuous operation , gas chromatographic analysis of the product showed the conversion of 2 - methylglutaronitrile to be that 95 %. the selectivity to 1 , 3 and 1 , 5 - dimethylpiperidone - 2 was 68 %. the byproduct selectivity to 1 , 3 - dimethyl - piperidine ; bis - 1 , 5 -( methylamido )- 3 - methylpentane ; 3 - and 5 - methylpiperidone - 2 and other high boilers was 12 %, 1 %, 2 . 2 % and 11 %, respectively . this example shows a continuous stirred tank reactor hydrogenation of 2 - methylglutaronitrile to 1 , 3 and 1 , 5 - dimethylpiperidone - 2 according to the present invention . 100 ml of a 40 % by weight solution of methylamine and 3 grams wet of a 50 % by weight of catalyst having 5 % by weight palladium on carbon powder were charges into a 300 cc stainless steel autoclave . the autoclave was equipped with a magadrive stirrer , a cooling coil , a thermocouple and a dip tube for product removal . after charging the autoclave , the reactor was sealed and purged with hydrogen three times . the sealed , purged autoclave was heated to 180 ° c . and pressurized to 34 bars with hydrogen . stirring was then started at 1000 rpms . a stream of 99 . 5 % by weight 2 - methylglutaronitrile ( available from e . i . dupont de nemours and company , inc . wilmington , del .) was fed into the autoclave at the rate of 10 ml / hour while a second stream of 40 % aqueous methylamine was fed into the autoclave at a rate of 8 . 8 ml / hour . the hold - up time was 5 hours . the flow of hydrogen was 250 cc / minute . a product stream was then drawn off at the rate of 17 . 6 ml / hour and sent to a 2 liter stainless steel pot as described in example 1 . as in example 1 , the concentrations of a water solution of a primary alkylamine , 2 - methylglutaronitrile and the 1 , 3 and 1 , 5 - dimethylpiperidone - 2 homogenizing solvent in the initial reaction mixture fell within the weight percents required by fig1 . after 161 hours running time with product take - off , the pressure in the autoclave was raised to 54 . 4 bars ( 800 psi ). as in example 1 , as product was taken - off , the rate of product take - off and the rate of reactant feed was balanced so that the concentrations of a water solution of a primary alkylamine , 2 - methylglutaronitrile and the 1 , 3 and 1 , 5 - dimethylpiperidone - 2 homogenizing solvent continued to fall within the weight percents required by fig1 . after 304 hours on stream , gas chromatographic analysis of the product showed the conversion of 2 - methylglutaronitrile to be that 92 %. the selectivity to 1 , 3 and 1 , 5 - dimethylpiperidone - 2 was 68 . 7 %. the byproduct selectivity to 1 , 3 - dimethylpiperidine ; bis - 1 , 5 -( methylamido )- 3 - methylpentane ; 3 - and 5 - methylpiperidone - 2 and other high boilers was 9 . 5 %, 3 . 5 %, 9 . 0 % and 13 . 3 %, respectively . this examples shows a batch hydrogenation of 2 - methylglutaronitrile to 1 , 3 - and 1 , 5 - dimethylpiperidone - 2 employing a homogenizing solvent of n - methylpyrrolidone . into a 300 ml stainless steel autoclave was charged 38 grams of 2 - methylglutaronitrile , 49 ml of a 40 % aqueous methylamine solution , 2 . 3 grams of water , 60 g n - methylpyrrolidone and 1 . 5 g of a 5 % palladium on carbon catalyst ( 4 . 0 % catalyst loading based on 2 - methylglutaronitrile ). the reactor was closed and purged twice with nitrogen and hydrogen and then pressured to 100 psig with hydrogen at room temperature . the mass was heated to 180 ° c . and pressured to 34 bars ( 500 psig ) with hydrogen and the agitator turned on to 1100 rpm . hydrogen uptake was monitored by a transducer connected to a recorder . the reduction required 120 minutes . after that time no additional hydrogen uptake was observed . gc analysis of the reaction mass showed complete conversion of 2 - methylglutaronitrile . the selectivity to 1 , 3 - and 1 , 5 - dimethylpiperidone - 2 was 56 . 7 %. the byproduct selectivity to 1 , 3 - dimethylpiperidine ; bis - 1 , 5 -( methylamido )- 3 - methylpentane ; 3 - and 5 - methylpiperidone - 2 and other high boilers was 7 %, 2 . 4 %, 1 . 7 % and 29 . 9 %, respectively . this example shows the hydrogenation of 2 - methylglutaronitrile to 1 , 3 - and 1 , 5 - dimethylpiperidone - 2 in the absence of a homogenizing solvent . into a 300 ml stainless steel autoclave equipped with a stirrer was charged 60 g 2 - methylglutaronitrile , 80 . 3 ml of a 37 . 8 % aqueous methylamine solution and 4 . 8 g of a 5 % palladium on carbon catalyst ( 4 . 0 % catalyst loading based on 2 - methylglutaronitrile ). the reactor was closed and purged twice with nitrogen and hydrogen and then pressured to 100 psig with hydrogen at room temperature . the mass was heated to 180 ° c . and pressured to 34 bars ( 500 psig ) with hydrogen and the agitator turned on to 1100 rpm . hydrogen uptake was monitored by a transducer connected to a recorder . the reduction required 240 minutes after which time no additional hydrogen uptake was observed . gc analysis of the reaction mass showed complete conversion of 2 - methylglutaronitrile . the selectivity to 1 , 3 - and 1 , 5 - dimethylpiperidone - 2 was 43 . 5 %. the byproduct selectivity to 1 , 3 - dimethylpiperidine ; bis - 1 , 5 -( methylamido )- 3 - methylpentane ; 3 - and 5 - methylpiperidone - 2 and other high boilers was 1 . 0 %, 42 . 1 %, 2 . 0 % and 15 %, respectively . table i below shows a comparison of selectivity of the prior art and the present invention . reaction conditions are shown in the table . the reaction conditions of the present invention are shown in entries 9 to table 1______________________________________ mol . wt wt . press 172 dpmdcatalyst % temp ., ° c . psig solvent % sel % sel no______________________________________5 % pd / c 4 . 0 180 500 none 32 . 1 53 . 4 15 % pd / c 0 . 5 180 500 none 42 . 1 43 . 5 24 . 5 % pd / 3 . 2 200 800 none 31 . 8 43 . 6 30 . 5 % pt / c5 % pd / c 2 . 8 180 800 none 17 . 0 55 . 5 45 % pd / c 2 . 0 180 1500 none 30 . 5 52 . 7 55 % pd / c 4 . 0 180 1000 none 26 . 9 57 . 3 65 % pd / c 4 . 0 180 2000 none 20 . 2 54 . 6 74 . 5 % pd / 6 . 4 200 800 none 33 . 5 49 . 6 80 . 5 % pt / c5 % pd / c 3 . 2 180 500 nmp 1 . 5 54 . 7 94 . 5 % pd / 4 . 3 190 500 nmp 7 . 5 69 . 6 100 . 5 % pt / c4 . 5 % pd / 4 . 7 200 800 nmp 4 . 8 53 . 4 110 . 5 % pt / c4 . 5 % pd / 3 . 2 200 800 nmp 6 . 7 58 . 5 120 . 5 % pt / c______________________________________ in the table : mgn conversions are & gt ; 95 %; nmp stands for nmethylpyrrolidone ; dmpd stands for dimethylpiperidone2 ; mol wt 172 stands for the byproduct bis1 , 5 -( methylamido )- 3 - methylpentane since this is the molecular weight of the byproduct . fig2 shows selectivities of bis - 1 , 5 -( methylamido )- 3 - methylpentane in both continuous stirred tank ( cstr ) and continuous trickle 15 bed operation over 200 hours of operation at mgn conversions of 90 %. for the continuous processes which are the process of the present invention , the selectivity is low to bis - 1 , 5 -( methylamido )- 3 - methylpentane compared to batch operation of the prior art which requires no homogenizing solvent .