The Use of Semimicro Technic in Organic Chemistry-V Catalytic Hydrogenation of Aldehydes and Ketones at Atmospheric Pressure NICHOLAS D. CHERONIS and NATHAN LEVIN Chicago City College, Chicago, Illinois I N A previous paper1 a general method for semimicro hydrogenation a t atmospheric pressure was de- scribed, with particular application to the reduction of nitro compounds. The present paper describes the extension of this method to the reduction of carbonyl compounds. The reduction of aldehydes and ketones has been extensively investigated, and the literature2-'[ cited does not include patents or catalytic hydrogena- tions at high temperatures and pressures. Though it has been possible to reduce aldehydes and ketones at pressures of 3 to 5 atmospheres, catalysts of high ac- tivity are required; furthermore, it has been observed that there is rapid decay in the activity of the catalyst, which can be somewhat offset by adding.a promoter. To the authors' knowledge the successful hydrogenation of the common aldehydes and ketones at atmospheric pressures, using a simple apparatus, has not been re- ported. Forrestis reported the rates of the hydrogena- tion of 1 ml. of acetophenone and benzophenone using an elaborate apparatus. From the velocity reported the time estimated for the reduction of 1 ml. of acetophe- none is 7 hours. Of the catalysts reported thus far in the present method of hydrogenation platiuic oxide was found to be the most efficient. Fifty milligrams of the catalyst were in most cases found sufficient to reduce 1 g. of the nitro compound within 20 to 30 minutes. It was noted early in this work that the activity of the various lots of pla- tinic oxide varied widely. The activity can be measured qualitatively by noting the time required for the re- duction of a deiinite amount of p-nitrophenol. The end of the reduction is evident from the disamearance of the . . . .. . . .. 182, 138 (1926): ' * ZELINSKY AND TARASSOWA, Ber., 65, 1249 (1932). PARKENDORPP, Ber.. 66, 872 (1933). l D ~ ~ ~ ~ ~ ~ ~ AND HOREAU, Compt. rend.. 201, 1301 (1935); 202,995 (1936); Bull. soc. chim., (5) 4, 31 (1937). 9 FORREST& Ann. chim. applicata, 26,207 (1936). 10 FOKREST~ AND CHIUMMO, GQZZ. chim. itel., 67, 408 (1937). "FORREST=_ CKIUMMO. AND MENASSE. Ann. chim. abblicatn. - ~ - ~ - ~ - ~ ~ . ~. . . 27,359 (1937). 1% DUPONT, BJI. SUC. chim., (5) 3, 1021 (1936). ~%KINO, J. Sac. Chem. Ind., Japan, 41, Supp. 259: ibid.. 42, yellow-green color of the solution; a melting-point de- termination of the product gives information as to the extent of the reduction.' Work by one of us, which will be published later, on the coagulation of platinum black indicates that the inactivity of the coagulated form of the catalyst is not due to the absence of o~ygen'9,~~ but to the saturation of the platinum particle with adsorbed active hydrogen. It is postulated that the active hy- drogen imparts a small charge to the particles of the catalyst and this eventually leads to coagulation. By bubbling air through the coagulated catalyst the active hydrogen is removed through combination with oxygen, and therefore the catalyst is dispersed and the activity regenerated. The same effect is produced by substances which can accept active hydrogen and can be reduced. In order to retard the coagulation of the finely divided platinum black a large number of experi- ments were performed with platinum black precipitated on finely divided carbon, silica, and other easily sns- pendable materials. It was found that the amount of platinum could be reduced to one fourth and still obtain the same activity as given by the most efficient of the platinic oxide catalysts. Using 250 mg. of 5 per cent platinum charcoal (containing 12.5 mg. Pt) the same re- duction rate was obtained as when 50 mg. of platinic oxide were employed. From these data it was con- cluded that for this type of semimicro hydrogenation platinum and palladium catalysts precipitated on car- bon are more economical and efficient. PLATINIZED AND PALLADIZED CARBONS A large number of platinum and palladium catalysts precipitated on carbon and other media were prepared or obtained commercially. To test their activity to- ward the reduction of aldehydes and ketones, piperonal and benzophenone were selected. Piperonal is known to be reduced easily and benzophenone with difficulty by catalytic hydrogenation. Therefore, both small and high activity could be qualitatively measured by sub- jecting the same catalyst for activity in the reduction of those two compounds. The extent of reduction was measured by removing 1 ml. of the solution, evaporating on a watch glass, and determining the melting point of the resulting product. Figure 1 shows the melting- point composition diagram of piperonal and piperonyl alcohol; Figure 2 shows the melting-point composition I* WILLSriiTrERAND JAQUET, Ber., 51, 767 (1918). " WILLS~ATTER AND WALDSHMIDT-LEITZ. Ber.. 54, 113 (1921).
Transcript
The Use of Semimicro Technic in Organic Chemistry-V
Catalytic Hydrogenation of Aldehydes and Ketones at Atmospheric Pressure
NICHOLAS D. CHERONIS and NATHAN LEVIN
Chicago City College, Chicago, Illinois
I N A previous paper1 a general method for semimicro hydrogenation a t atmospheric pressure was de-
scribed, with particular application to the reduction of nitro compounds. The present paper describes the extension of this method to the reduction of carbonyl compounds. The reduction of aldehydes and ketones has been extensively investigated, and the literature2-'[ cited does not include patents or catalytic hydrogena- tions a t high temperatures and pressures. Though it has been possible to reduce aldehydes and ketones at pressures of 3 to 5 atmospheres, catalysts of high ac- tivity are required; furthermore, it has been observed that there is rapid decay in the activity of the catalyst, which can be somewhat offset by adding.a promoter. To the authors' knowledge the successful hydrogenation of the common aldehydes and ketones a t atmospheric pressures, using a simple apparatus, has not been re- ported. Forrestis reported the rates of the hydrogena- tion of 1 ml. of acetophenone and benzophenone using an elaborate apparatus. From the velocity reported the time estimated for the reduction of 1 ml. of acetophe- none is 7 hours.
Of the catalysts reported thus far in the present method of hydrogenation platiuic oxide was found to be the most efficient. Fifty milligrams of the catalyst were in most cases found sufficient to reduce 1 g. of the nitro compound within 20 to 30 minutes. It was noted early in this work that the activity of the various lots of pla- tinic oxide varied widely. The activity can be measured qualitatively by noting the time required for the re- duction of a deiinite amount of p-nitrophenol. The end of the reduction is evident from the disamearance of the
yellow-green color of the solution; a melting-point de- termination of the product gives information as to the extent of the reduction.' Work by one of us, which will be published later, on the coagulation of platinum black indicates that the inactivity of the coagulated form of the catalyst is not due to the absence of o ~ y g e n ' 9 , ~ ~ but to the saturation of the platinum particle with adsorbed active hydrogen. It is postulated that the active hy- drogen imparts a small charge to the particles of the catalyst and this eventually leads to coagulation. By bubbling air through the coagulated catalyst the active hydrogen is removed through combination with oxygen, and therefore the catalyst is dispersed and the activity regenerated. The same effect is produced by substances which can accept active hydrogen and can be reduced. In order to retard the coagulation of the finely divided platinum black a large number of experi- ments were performed with platinum black precipitated on finely divided carbon, silica, and other easily sns- pendable materials. It was found that the amount of platinum could be reduced to one fourth and still obtain the same activity as given by the most efficient of the platinic oxide catalysts. Using 250 mg. of 5 per cent platinum charcoal (containing 12.5 mg. Pt) the same re- duction rate was obtained as when 50 mg. of platinic oxide were employed. From these data it was con- cluded that for this type of semimicro hydrogenation platinum and palladium catalysts precipitated on car- bon are more economical and efficient.
PLATINIZED AND PALLADIZED CARBONS
A large number of platinum and palladium catalysts precipitated on carbon and other media were prepared or obtained commercially. To test their activity to- ward the reduction of aldehydes and ketones, piperonal and benzophenone were selected. Piperonal is known to be reduced easily and benzophenone with difficulty by catalytic hydrogenation. Therefore, both small and high activity could be qualitatively measured by sub- jecting the same catalyst for activity in the reduction of those two compounds. The extent of reduction was measured by removing 1 ml. of the solution, evaporating on a watch glass, and determining the melting point of the resulting product. Figure 1 shows the melting- point composition diagram of piperonal and piperonyl alcohol; Figure 2 shows the melting-point composition
(6) platinized and palladized carbon are much more ac- tive than equal amounts of metal in the form of "re- duced black" obtained from the oxide; (c) palladium and platinum carbons prepared by reduction with hy- drazine a t low temperatures have a higher activity than when reduced at elevated temperatures or reduced by formaldehyde a t either high or low temperatures; (d) commercially available 5 per cent palladium carbon was found to have about the same activity as the more active sample prepared; (e) for complete reduction of benzophenone a nickel oxide catalyst and palladium carbon are necessary; and ( j ) platinized oxides of nickel-iron manganese (Pt: Me0 = 1: 8) have higher activity than Raney nickel or platinized Raney nickel.
SOLVENT AND PH EPPECT
The use of an alcohol as a solvent for catalytic hy- drogenation of aldehydes and ketones is sometimes not desirable. Such an occasion may arise in the identifi- cation of a carbonyl compound, when the latter is re- duced to the alcohol which is then subjected to deriva- tization. It was considered, therefore, of some interest to test the effect of various solvents in the reduction of piperonal, using the same catalyst throughout. The results are summarized in Table 3. Since the object of
TABLE 3
AYDI(OCBNATI0N On PKPEBONAL* IN VARIOUS SOLYBNTS I N PRBSBNCB OF P*LLADI"M CARBON^
8 Five hvndred milligrams of piperonnl dissolved in 25 ml. of the solvent; 250 mg. of catalyst added and hydrogen passed for 10 minutas nt the rate of 1Wto 125 ml. per minute.
t Carbon containing 5 per cent palladium (Baker and Company). t After filtration of catalyst thesolvent was evawrated, the melting point
of the product determined, and extent of reduction determined fmm Figure 1. t Productsahich without reqystallirationgave melting points of 48-52'C.
arereported as 100 per cent redlued. II Results not consirfcof; product is oftcn an oil which does not uyatnllire.
the experiments was to discover a nonaqueous and non- alcoholic solvent for semimiao hydrogenation, the data are given without discussion as to their probable explanation. Suffice it to state that the efficiency of the solvent was found to be: ethanol > 2-propanol > esters > ethers > hydrocarbons. Esters were found to react with such reagents as 3,5-dinitrobenzoyl chloride and a-naphthyl isocyanate. Isopropyl ether was se- lected as a solvent when a derivative of the alcohol re- sulting from the reduction of the carbonyl compound was to be prepared.
The &ect of alkaline media on the reduction of ke- tones has been noted by Delepine,8Forresti,g and others.
The object of the experiments summarized in Table 4 was to determine the &ect of change of the pH in the semimicro hydrogenation of ketones using the catalysts and method developed. The results indicated that an initial pH above 8 increases the rate of reduction, while an initial pH of below 7.0 inhibits the reaction.
The carbonyl compounds successfully reduced by this method and the condition of hydrogenation are listed in Table 5. The reduction of acetone and butanone in the presence of isopropyl ether is incomplete. In gen- eral the reduction in isopropyl ether is slow and not suitable for rapid microhydrogenation of the aliphatic carbonyl compounds. Aromatic aldehydes and ketones are reduced with varying rates, the ortho-substituted al- dehydes having the most rapid. The reduction of piperonal and salicylaldehyde is suitable for prepara- tive work to illustrate catalytic hydrogenation of car- bony1 compounds, and detailed directions are given in the experimental part. For the reduction of ketones a nickel oxide catalyst should be used in conjunction with palladium carbon.
EXPERIMENTAL PART
General Method. The general directions for semimicro hydrogenation are the same as previously described.' The commercial model of the hydrogenating tube21 shown diagrammatically in Figure 3 was used in the present investigation. The student model1 may be used for the reduction of piperonal and salicylaldehyde. The commercial grade of 5 per cent palladium black is efficient and is recommended for the reduction of nitro compounds in which the platinic oxide catalyst was pre- viously' specified. After reduction the solution is 61- tered; the first filtrate is returned to the filter as a small amount of finely divided carbon passes through. When the filtration is complete the paper is washed twice with 5 ml. of the solvent used in the reduction. The funnel is removed and water is drained off, and the paper is pressed together and placed in a bottle. When a snffi- cient number of papers have accumulated, they are burned and the carbon and ash returned to the dealer for
The cost of 5 per cent palladium carbon in 10-g. lots is $0.25 per gram and therefore the cost of catalyst per run is $0.06.
Materials. Commercial zinc and 25 per cent sulfuric acid were used to eenerate hvdroeen. Most of the or- - < " -
21 Wilkens-Anderson Company, Chicago, Illinois. (See Fig; ure3.)
which has been previously boiled with 20 per cent so- dium hydroxide solution, then with water, washed free of alkali, and dried. The metallic oxide catalyst pre- pared by this method is pyrophoric and care should be taken in weighing it. To remove i t from the tube use a long spatula and avoid tilting the tube so that the car- bon falls out into the weigh in^ vessel, for in that case i t will catch fire. This catahst used in conjunction with palladium carbon in the reduction of ketones. Alde- hydes undergo other changes in its presence, probably because of its slight alkalinity.
Determination of Melting Points of Substances or Mix- lures Which Melt Between -50° and +4Q°C. This method is useful for the determination of melting points of substances or entectic mixtures which are liquid a t ordinary temperatures.
Apparatus used in the determination is shown in Fig- ure 4. It consists of an &inch tube with a side arm hav- ing the closed end blown to a bulb of 35 to 40 mm. in di- ameter and having a capacity of 25 to 30 d. The commercial model2' has a small glass tuhe reaching from the side arm to the bottom of the tube, curving upwards, and ending in an orifice of about 0.3 to 0.5 mm. for blowing a stream of bubbles. The same pur-
capillary is inserted in the melting-point tube to be used as a stirring rod for the crystallization.
If the melting point of the solid is above -15°C. an intimate mixture of ice and salt is placed in a 50- or 100- ml. beaker and the melting-point tube is immersed and allowed to remain for three to five minutes. When the liquid has crystallized, the melting-point tuhe is re-
pose can be accomplished by inserting through the top of the apparatus a 4-mm. tube drawn to a capillary a t the end and bent a t a right angle a t the top. A 3-mm. rubber tube is connected to the inlet and held a t the mouth for blowing a stream of bubbles. An alcohol- filled thermometer, graduated from -50' to +50°C. is ' inserted through a cork which is held by a clamp so that the end of the thermometer bulb is 10mm. from the bot- tom. About 25 to 30 d. of methanol are added to the bulb to serve as bath liquid.
A capillary tube, 1 mm. in outer diameter and 75 to 80 mm. in length,%% is sealed a t one end to serve as melting-point tube. Another.capilIary tube having an outer diameter of 0.2 to 0.4 mm., length of 110 to 120 rnm., and openings a t both ends, is prepared. The smaller capillary should be inserted in the melting- point tube so that one end reaches the bottom freely. A small droplet of the liquid (1 mg. or less) is placed on a small watch glass. Holding the melting-point tube with one hand remove the smaller capillary and place it ver- tically so that one end of the open capillary is immersed in the liquid which, by capillary attraction, rises rap- idly into the tube to a height of 40 to 50 mm., depending on the diameter of the capillary and properties of the liquid. The smaller capillary is inserted in the melting- point tuhe and pushed gently down until the end reaches the bottom. This pressing gently downwards rotates the smaller capillary so that the liquid descends and fills the melting-point tube to a height of 3 to 4 mm., when the capillary is rapidly withdrawn, streaking the sides of the melting-point tube with the oil in passing. , The clean end of the smaller capillary is held momentarily in the flame so that the open end is just sealed off, form- ing a very small head a t the end. The sealed end of the - " These capillary tubes are commercially available packed in vials containing 100 capillaries. They can he used in all melting- point determinations.
moved and the lower end is held momentarily between two fingers so as to melt the crystals partially. The melting-point tuhe is replaced in the ice-salt bath and the mixture of crystals and liquid is stirred by raising and lowering the capillary rod until the mass begins to solidify, when the capillary rod is withdrawn. The lower end of the melting-point tube thus contains a crystalline mass while the sides are covered by a film of crystals to a height of 10 to 20 mm., giving a foggy ap- pearance to the tube. When the tuhe is heated this foggy film of crystals vanishes suddenly, furnishing thereby a better criterion of the temperature a t which melting takes place.
When the liquid does not crystallize because of su- percooling, the liquid is rubbed against the walls of the vessel with the capillary stirring rod. Some substances require considerable agitation before they begin to crystallize. Seeding may be used to induce crystalliza- tion. The watch glass on which the dropIet was placed for transfer to the capillary is chilled by placing it on the freezing mixture and rubbing i t with a spatula. As soon as crystals have formed, the capillary rod is withdrawn from the tube and the head a t its end is touched to a few
minute crystals and then transferred back to the melt- ing-point tube. If the melting point of the substance is between -IS0 and -50°C. the bath used is a mixture of dry ice and acetone or methanol. About 75 ml. of the acetone or alcohol are placed in a 250-ml. beaker wrapped in a towel, and then small pieces of dry ice are added until the required temperature has been reached.
While the meltine-ooint tubc is bcinr ~rcnsred the bulb - A -.
of the melting-point apparatus is immersed in a cooling mixture similar to that used for chilling the melting- point tube. A 250-ml. beaker is used; the bulb with the thermometer resting on the bottom is immersed in the cooling mixture and stirred occasionally with the ther- mometer. When the temperature has fallen about 10' below the melting point of the compound in the capil- lary tube the thermometer is transferred rapidly close to the melting-point tube, which is attached to the ther- mometer bya rubber band. The melting-point apparatus is removed from the cooling bath and clamped in posi- tion on the stand; the thermometer is removed from the coqling bath, lightly shaken to remove adhering liquid, and rapidly adjusted in place within the liquid bath of the melting-point apparatus. The bulb is wiped off with a dry cloth and the melting-point tube in- spected. If the operations have been made with proper care the temperature is several degrees below the melt- ing point and any solid that may have melted during the adjustments has solidifled. The bath is heated by holding the small rubber tube' between the lips and blowing a stream of bubbles intermittently through the liquid. The temperature rises about lo for every one or two minutes. If more rapid heating is required, as when the temperature is much below the melting point, the bulb is warmed by holding it in the hand for a few sec- onds or by momentarily applying the smallest flame of a microhurner. When the foggy film above the mass of crystals in the melting-point tube vanishes, further heating or blowing "bubbles" through the bath is dis- continued and the temperature noted. If the com- pound is pure the crystals melt within 0.5' of this tem- perature. If the crystals are impure the mass may not melt completely until the temperature has been raised several degrees above this point.
Reduction of Pifierunel. Place 250 mg. of 5 per cent
palladium carbon in the hydrogenating tube and add 25 ml. of ethanol. Pass hydrogen for two minutes and then add 500 mg. of piperonal. Heat the bath to 6OoC. and pass hydrogen for 15 minutes. Filter and wash residue with two 5-ml. portions of alcohol. Evaporate the filtrates in a dish over a water bath until a small amount of solvent remains, then conduct the evapora- tion slowly. Cool the residual oil by placing the dish in a freezing mixture. On scratching the oil with the spat- ula i t solidifies. Scrape the crude mass and transfer i t into a tube. Add 12 to 15 ml. of heptane or petroleum ether. Boil to effect solution and filter through suc- tion into an 8-inch test tube having a side arm. The oily mass remaining in the solution tube is crude piper- onyl alcohol and is extracted using the filtrates from the first crystallization. Cool the filtered solution and scratch the sides of the tube with a glass rod. Allow to stand 10 minutes and filter. Conduct successive ex- tractions of the crude piperonyl alcohol, using the fil- trates from the previous crystallization, until the crude residue is exhausted. Collect the crystals on the suction funnel and wash with a few milliliters of the pure sol- vent. Place the crystals on a drying disc. Yield: about 400 mg. of crystals melting a t 52-53'C.
Reduction of Salicylaldehyde. Use the same method and quantities as in the reduction of piperonal. Pass hydrogen for 25 to 30 minutes. Use the same method for the purification of the crude alcohol but use 20 ml. of solvent. Yield: 350 to 400 mg. of crystals melting a t 86°C.
Reduction of Benzofihenone. Place in the hydrogenat- ing tube 25 ml. of ethanol, 100 mg. of 5 per cent palla- dium carbon, and 450 mg. of nickel-iron carbon. Pass hydrogen for two minutes and then add 200 mg. of ben- zophenone. Pass hydrogen for 30 minutes. Filter the carbon and wash the residue with two 5-ml. portions of alcohol. Evaporate the' alcohol in a dish. Cool and scratch the oil mass with the microspatula. Collect the crystals on the bottom of the aish and transfer them into a tube. Wash the dish with 5 ml. of heptane or pe- troleum ether, and add the solvent to the tube contain- ing the crude benzohydrol; heat the mixture to boiling and filter through suction into an &inch tube with a side arm. Cool the solution and scratch the sides of the ves-
M.P. or B.P. Amf. Tina Cor&onrl Compound ( " C ) ( M d Salvrnl (Mix.)
Cyeloh~xnnal (3) Benryl alcohol ( 8 ) Salieyl alcohol (A) P-Hydroxybenzyl yllceohol ( A ) Piperooyl alcohol ( A ) Vanillvl alcohol ( A )
M.P. of Product or Dniaoliae*
( T I Obs. Lit.
. . * Unless otherwise npecificd 250 mg. of 5 p u cent pdladium carbon was used as catalyst. t 250 mg. of 5 per cent Pd carbon and 400 mg. of carbon containing oxides of Ni, Pe, Mn. See Experimental Part. ( A ) = correrponding alcohol; [B) - 3,5-dioitmbenroate; ( C ) = o-Naphthylurcthan.
sel with a glass rod. After 10 minutes filter the crystal and wash with 1 ml. of pure solvent. Use the filtrates to extract the remaining crude benzohydrol. Yield: 100 to 150 mg. of crystals melting a t 6748OC.
Reduction of Benzaldehyde. Place 29 ml. of isopropyl ether and 250 mg. of 5 per cent palladium carbon in the hydrogenating tube. Pass hydrogen for two minutes and then add 0.25 ml. of benzaldehyde. Raise the tem- perature of the bath to about 50°C. and pass hydrogen for 20 minutes. Filter the isopropyl ether solution into an &inch distilling tube or 25-ml. distilling flask; add 150 mg. of 3,5-diuitrobenzoyl chloride and distill off the ether until about 2 ml. remain in the distilling
vessel. Pour off the ether solution into a dish and wash the distilling vessel with 1 to 2 ml. of isopropyl ether, adding the washings to the residue in the dish. Add 2 ml. of water and evaporate to dryness. Cool, add 5 ml. of water, and transfer crystalline mass into the filter. Return crystals to the dish and rub well with 5 ml. of 5 per cent sodium carbonate solution, warm to 60°C., then filter, and wash twice with water. Recrystallize from methanol. Yield: 80 mg. of crystals melting a t 109-llO°C. On crystallizing again, 50 to 55 mg. are obtained melting a t 112'C.
Heptanal and other aliphatic aldehydes are reduced in the same manner for identification purposes.
