I hope You all like it. I hope It is very beneficial for you all. I really thought that you all get enough knowledge from this presentation. This presentation is about materials and their classifications. After you read this presentation you knowledge is not as before.

1. The Art of HeterogenousThe Art of Heterogenous
Catalytic HydrogenationCatalytic Hydrogenation
Part 1Part 1
An Introduction:An Introduction:
Chemistry 536Chemistry 536

2. Recommended Books:Recommended Books:
 Heterogenous Catalysis for the SyntheticHeterogenous Catalysis for the Synthetic
ChemistChemist

Robert L Augustine (1996)Robert L Augustine (1996)
 Practical Catalytic Hydrogenation,Practical Catalytic Hydrogenation,
Techniques and ApplicationsTechniques and Applications

Morris Freifelder 1971Morris Freifelder 1971

3. Recommended ReferencesRecommended References
 Catalytic Hydrogenation over PlatinumCatalytic Hydrogenation over Platinum
MetalsMetals

P. N. Rylander 1967P. N. Rylander 1967

4. What will Not be Covered Here:What will Not be Covered Here:
(Topics for Another Class)(Topics for Another Class)
 Homogenous catalystsHomogenous catalysts
 Chiral catalysisChiral catalysis

5. What will be Covered Here:What will be Covered Here:
 Some basic theorySome basic theory
 CatalystsCatalysts
 Solvents, and their effectsSolvents, and their effects
 Structure effectsStructure effects
 Temperature effectsTemperature effects
 Common and useful reductions with hydrogenCommon and useful reductions with hydrogen
 How to use a Parr ShakerHow to use a Parr Shaker
 Tour of the High Pressure LabTour of the High Pressure Lab

6. Two Ways to Add Hydrogen:Two Ways to Add Hydrogen:
 Hydrogenation:Hydrogenation:
addition across Piaddition across Pi
bondsbonds
 Hydrogenolysis:Hydrogenolysis:
Cleavage of SigmaCleavage of Sigma
bondsbonds
A Y A Y
H H
A X A X
H H

7. Catalysts: OverviewCatalysts: Overview
 Discrimination dependent upon:Discrimination dependent upon:

MetalMetal

SupportSupport

SolventSolvent

TemperatureTemperature

Presence or absence of poisonsPresence or absence of poisons

PromotersPromoters

8. Catalysts Overview, cont’d:Catalysts Overview, cont’d:
 Rate of reduction dependent upon:Rate of reduction dependent upon:

Catalyst preparationCatalyst preparation

Time (in hours) since prep. of catalystTime (in hours) since prep. of catalyst

PressurePressure

TemperatureTemperature

Loading of catalystLoading of catalyst

9. Why Choose CatalyticWhy Choose Catalytic
Hydrogenation?Hydrogenation?
 Simple work-upSimple work-up
 Generally clean reactionsGenerally clean reactions
 No extra ions or compounds to deal with;No extra ions or compounds to deal with;
just remove solvent.just remove solvent.
 Can be done neat.Can be done neat.
 Most cost-effective choice for scale-upMost cost-effective choice for scale-up
 In Process; spent catalyst is usuallyIn Process; spent catalyst is usually
recoverable for cost savingsrecoverable for cost savings

10. RheniumRhenium
 Usually used in an oxide form (recoveredUsually used in an oxide form (recovered
in an oxide form)in an oxide form)
 Requires vigorous conditionsRequires vigorous conditions
 Best use is in reduction of carboxylic acidsBest use is in reduction of carboxylic acids
to alcohols or amides to aminesto alcohols or amides to amines
 Typical conditions: 200 atm and 150-250Typical conditions: 200 atm and 150-250
°C°C

11. RutheniumRuthenium
 Used as dioxide or metal on supportUsed as dioxide or metal on support
 Commercially availableCommercially available
 Active at 70-80Active at 70-80 °C/ 60-70 atm°C/ 60-70 atm
 Very resistant to poisoningVery resistant to poisoning
 Good choice for reduction of aromatic rings, butGood choice for reduction of aromatic rings, but
does not discriminate.does not discriminate.
 Reduces COOH, but only at HP; 500-950 atm.Reduces COOH, but only at HP; 500-950 atm.
 Reduces aldehydes, ketones, even sugars.Reduces aldehydes, ketones, even sugars.

12. Copper Chromium OxideCopper Chromium Oxide
 Commercially availableCommercially available
 Useful only at elevated temperatures andUseful only at elevated temperatures and
pressures (250-300pressures (250-300 °C/250-300 atm)°C/250-300 atm)
 Used for reduction of aldehydes andUsed for reduction of aldehydes and
ketones w/o hydrogenolysisketones w/o hydrogenolysis
 No effect on benzene ringNo effect on benzene ring
 Used for reduction of amides to aminesUsed for reduction of amides to amines
and esters to alcohols, but now replacedand esters to alcohols, but now replaced
with LAHwith LAH

13. CobaltCobalt
 Mostly used in “Raney” formMostly used in “Raney” form
 Active primarily at elevated pressures andActive primarily at elevated pressures and
temperaturestemperatures
 Converts nitriles to primary aminesConverts nitriles to primary amines
(absence of ammonia)(absence of ammonia)
 Can reduce double bonds and carbonylsCan reduce double bonds and carbonyls
at 1 atm, but much less active than Raneyat 1 atm, but much less active than Raney
NickelNickel

14. Just what are Raney metals?Just what are Raney metals?
 An alloy of the metal and aluminum is made byAn alloy of the metal and aluminum is made by
melting them together a certain proportions.melting them together a certain proportions.
 The aluminum is dissolved away using sodiumThe aluminum is dissolved away using sodium
hydroxide solutionhydroxide solution
 The remaining metal from the alloy “domains”The remaining metal from the alloy “domains”
become particles with high surface area and arebecome particles with high surface area and are
charged with hydrogencharged with hydrogen
 It is extremely flammable in air and must beIt is extremely flammable in air and must be
handled wet with waterhandled wet with water
 Commercially available, but best if prepared justCommercially available, but best if prepared just
before use. (See Freifelder, p. 7)before use. (See Freifelder, p. 7)

15. NickelNickel
 Mostly used as Raney NickelMostly used as Raney Nickel
 Very subject to loss of activity within two weeksVery subject to loss of activity within two weeks
of preparation, especially W-6 and W-7of preparation, especially W-6 and W-7
 Only modest temperatures and pressuresOnly modest temperatures and pressures
neededneeded
 Can selectively reduce aromatic ringsCan selectively reduce aromatic rings
 Above 100Above 100 °C reaction may get out of hand°C reaction may get out of hand
 Reduces esters, ketones, nitrilesReduces esters, ketones, nitriles

16. Nickel cont’dNickel cont’d
 Other forms are nickel on kieselguhr andOther forms are nickel on kieselguhr and
form of Urushibara (form of Urushibara (Bull. Chem Soc. JapBull. Chem Soc. Jap
2525, 280 (1952)), 280 (1952))
 Can be used in acid solution (HOAc) andCan be used in acid solution (HOAc) and
can give better results than noble metalcan give better results than noble metal
catalysts (i.e. better discrimination andcatalysts (i.e. better discrimination and
yields)yields)

17. PlatinumPlatinum
 Don’t use platinum black: highly variableDon’t use platinum black: highly variable
 Adam’s catalyst (PtOAdam’s catalyst (PtO22)(Stable in storage!))(Stable in storage!)
and platinum on support are mostand platinum on support are most
common forms; all commercially availablecommon forms; all commercially available
 Wide variety of reductions, includingWide variety of reductions, including
hydrogenation and hydrogenolysis,hydrogenation and hydrogenolysis,
depending upon conditions; most are milddepending upon conditions; most are mild
 Poisoned by amines and sulfurPoisoned by amines and sulfur

18. Platinum cont’dPlatinum cont’d
 If PtOIf PtO22 is pre-treated with HOAc or MeOHis pre-treated with HOAc or MeOH
wash, can reduce benzene rings readily.wash, can reduce benzene rings readily.
 PtOPtO22 not selective between double andnot selective between double and
triple C-C bonds.triple C-C bonds.
 Many variants of Pt/C, each with its ownMany variants of Pt/C, each with its own
selectivity.selectivity.

19. PalladiumPalladium
 Many forms of palladium on supportMany forms of palladium on support
available, each with its own selectivityavailable, each with its own selectivity
 Less than half the cost of platinumLess than half the cost of platinum
 Gives both hydrogenation andGives both hydrogenation and
hydrogenolysishydrogenolysis
 Most reductions under mild conditionsMost reductions under mild conditions
 Subject to poisoning with sulfur, amines,Subject to poisoning with sulfur, amines,
and lead.and lead.

20. RhodiumRhodium
 Expensive (~Pt), but very versatile.Expensive (~Pt), but very versatile.
 Best for reductions of aromatic systemsBest for reductions of aromatic systems
(incl. heterocycles) under mild conditions(incl. heterocycles) under mild conditions
sans acidsans acid
 Reduces C=C, nitro, and carbonyls; mostReduces C=C, nitro, and carbonyls; most
reducible groupsreducible groups
 Aromatic vs carbonyl selectivity can beAromatic vs carbonyl selectivity can be
controlled by pH and nearby groupscontrolled by pH and nearby groups

21. Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons
 Inhibitors diminish the rate , but the effectInhibitors diminish the rate , but the effect
can be reversed by washing it away.can be reversed by washing it away.
 Poisons exert an appreciable inhibitoryPoisons exert an appreciable inhibitory
effect when present in small amounts.effect when present in small amounts.
 Both can be used to fine-tune theBoth can be used to fine-tune the
selectivity of a catalyst.selectivity of a catalyst.

22. Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons
 Metals and metals SaltsMetals and metals Salts
 Mg, Ni Co have no effect on PdClMg, Ni Co have no effect on PdCl22 reductions.reductions.

Al, Fe, Cu, Zn, Ag, Sn, Pb, Hg, Cr their oxidesAl, Fe, Cu, Zn, Ag, Sn, Pb, Hg, Cr their oxides
and carbonates inhibit Palladium.and carbonates inhibit Palladium.

Pt reductions inhibited by Al, Co, Bi.Pt reductions inhibited by Al, Co, Bi.

Pt Reductions increased by Fe, Cu Zn, Ag, PbPt Reductions increased by Fe, Cu Zn, Ag, Pb

Raney nickel completely inhibited by mercuricRaney nickel completely inhibited by mercuric
chloride, but 50% inhibited by Agchloride, but 50% inhibited by Ag22SOSO44

23. Catalyst Inhibitors and PoisonsCatalyst Inhibitors and Poisons
 Halogen-Containing CompoundsHalogen-Containing Compounds

Halide ions inhibit Ni, sometimes Pt, Pd: IHalide ions inhibit Ni, sometimes Pt, Pd: I--
>> Br>> Br--
> Cl> Cl--
> F> F--
in a concentration-dependent manner.in a concentration-dependent manner.
Corresponding acids just as potent, if anhydrous. Tip:Corresponding acids just as potent, if anhydrous. Tip:
add water or use acetic acid.add water or use acetic acid.

Non-ionizable organic halides often do not inhibit PtNon-ionizable organic halides often do not inhibit Pt
and Pd, except when directly bonded to the region ofand Pd, except when directly bonded to the region of
reduction (e.g. aromatic halides reduced toreduction (e.g. aromatic halides reduced to
cyclohexane halides).cyclohexane halides).

Potent inhibitors (Ni): carbon tet, chloroform, chloralPotent inhibitors (Ni): carbon tet, chloroform, chloral
hydrate, trichloroethanol, di- and trichloroacetic acid,hydrate, trichloroethanol, di- and trichloroacetic acid,
alkyl chloride, benzyl chloride, and acetyl chloride.alkyl chloride, benzyl chloride, and acetyl chloride.

24. An Example of Halide InhibitionAn Example of Halide Inhibition
N+
H+
N
HO HO
Cl-
Cl-
Pd/H2/EtOH
RT, 6 hours
N+
HO
I-
H+
N
HO
I-
X
Pd/H2/EtOH
120 C, 48 hrs,
900 psi
60 psi

25. Compounds containing Ar, Sb, O,Compounds containing Ar, Sb, O,
P, Se, TeP, Se, Te
 Oxygen rarely inhibits, except as COOxygen rarely inhibits, except as CO
 Other members of this group are inhibitorsOther members of this group are inhibitors
if their oxidation state leaves unbondedif their oxidation state leaves unbonded
electron pairs on the central atom.electron pairs on the central atom.
 Example: POExample: PO44
3-3-
InertInert
PHPH33 InhibitorInhibitor

26. Compounds containing Ar, Sb, O,Compounds containing Ar, Sb, O,
P, Se, Te cont’dP, Se, Te cont’d
 Sulfate: inertSulfate: inert
 Sulfite: InhibitorSulfite: Inhibitor
 Phosphite, hypophosphite: inhibitorPhosphite, hypophosphite: inhibitor
 AsHAsH33 and SbHand SbH33 are poisons, as well asare poisons, as well as
organic derivativesorganic derivatives
 Se and Te in lower oxidation states areSe and Te in lower oxidation states are
inhibitorsinhibitors

27. Sulfur as an InhibitorSulfur as an Inhibitor
 As sulfides, mercaptans, disulfides, andAs sulfides, mercaptans, disulfides, and
thiosulfates and thiophenes: potentthiosulfates and thiophenes: potent
inhibitors.inhibitors.
 Beware the rubber stopper! ContainsBeware the rubber stopper! Contains
sulfur for vulcanizing!sulfur for vulcanizing!
 Some sulfoxides and sulfinates areSome sulfoxides and sulfinates are
inhibitors.inhibitors.
 Sulfonates, sulfuric acid, and sulfoxidesSulfonates, sulfuric acid, and sulfoxides
have little effect.have little effect.

28. The Effect of the Nitrogen AtomThe Effect of the Nitrogen Atom

Compounds with unshielded basic Nitrogen act asCompounds with unshielded basic Nitrogen act as
inhibitors.inhibitors.

Compounds which generate basic nitrogen onCompounds which generate basic nitrogen on
reduction (e.g. nitro, oxime) act as inhibitors.reduction (e.g. nitro, oxime) act as inhibitors.

Nitrile is an inhibitor (likely due to product), whileNitrile is an inhibitor (likely due to product), while
cyanide is a catalyst poison.cyanide is a catalyst poison.

Non-basic nitrogens (e.g. in amide or urea) have littleNon-basic nitrogens (e.g. in amide or urea) have little
effect.effect.

Non-poisonous: Schiff-bases, imines, azines,Non-poisonous: Schiff-bases, imines, azines,
hydrazones & similar cpds with azomethine links.hydrazones & similar cpds with azomethine links.

29. Other Nitrogen InhibitorsOther Nitrogen Inhibitors

Pyridine and related heterocycles arePyridine and related heterocycles are
inhibitors.inhibitors.

Piperidine is a potent poisonPiperidine is a potent poison

Quinoline is only a weak inhibitor, often usedQuinoline is only a weak inhibitor, often used
for modifying activityfor modifying activity

30. Strategies to Counter the InhibitionStrategies to Counter the Inhibition
by Nitrogenby Nitrogen
 Use a protic solvent such as ethanol,Use a protic solvent such as ethanol,
methanolmethanol
 Use an organic acid such as acetic acidUse an organic acid such as acetic acid
 Use 1 equivalent HCl (less preferable)Use 1 equivalent HCl (less preferable)
 Choose an alternate catalyst notChoose an alternate catalyst not
susceptible to nitrogen inhibition (rarely ansusceptible to nitrogen inhibition (rarely an
option)option)

31. Using Catalyst PoisonsUsing Catalyst Poisons
 Effect of poisoningEffect of poisoning
agents not the sameagents not the same
for every catalystfor every catalyst
 Can be added to stopCan be added to stop
a multi-step reductiona multi-step reduction
at a given level ofat a given level of
reduction. Example :reduction. Example :
the Rosamundthe Rosamund
Reduction:Reduction:
Cl
O
H
O
PtO2/thiourea

32. Useful InhibitionUseful Inhibition
 Reduction ofReduction of
cinnamaldehyde to 3-cinnamaldehyde to 3-
phenylpropionaldehydephenylpropionaldehyde
(added pyridine limits(added pyridine limits
reduction):reduction):
 Lindlar reduction ofLindlar reduction of
acetylenes:acetylenes:
H
O
H
O
RaNi, H2, Pyridine
C13H27
OH
NO2
OH
C13H27
OH
NO2
OH
H
H
Pd/CaCO3, H2
Poison: lead acetate

33. Catalyst PromotersCatalyst Promoters
 Substances that produce greater catalytic effectSubstances that produce greater catalytic effect
than can be accounted for by each componentthan can be accounted for by each component
independently and in proportion to the amountindependently and in proportion to the amount
presentpresent
 Most promotors are inactive as catalystsMost promotors are inactive as catalysts
themselves.themselves.
 Sometimes are inactivators in another contextSometimes are inactivators in another context
and/or at a higher concentrationand/or at a higher concentration
 Promoters tend to be specific to an application.Promoters tend to be specific to an application.

34. Examples of promoters:Examples of promoters:
 Added CeriumAdded Cerium
distinctly promotesdistinctly promotes
the reduction ofthe reduction of
toluene:toluene:
 Addition of 1:1Addition of 1:1
Mol/mol FeClMol/mol FeCl33 to Ptto Pt
increases rate ofincreases rate of
reduction of nitroreduction of nitro
400%400%
175 C/ 125 atm
Nickel on Keiselguhr
R-NO2 RNH3
Pd or Pt/ H2

35. Metal PromotersMetal Promoters
 10 mole% FeCl10 mole% FeCl33 perper
g-atom Pt allowsg-atom Pt allows
reduction ofreduction of
Benzaldehyde at aBenzaldehyde at a
practical rate:practical rate:
 SnClSnCl22 promotes thepromotes the
reduction ofreduction of
heptaldehyde with Ptheptaldehyde with Pt
or PtOor PtO22::
Hydrogen/ PtO2
HO
OH
H
O
H
OH
H
PtO2/H2

36. Air as a promoterAir as a promoter
 Some reductions, esp. aldehydes over platinumSome reductions, esp. aldehydes over platinum
or ruthenium, are very slow if the mixture is notor ruthenium, are very slow if the mixture is not
periodically purged with air.periodically purged with air.
 Need may arise from depletion of “lower oxide”Need may arise from depletion of “lower oxide”
active form of platinum catalyst; purging withactive form of platinum catalyst; purging with
nitrogen has no effect.nitrogen has no effect.
 Pt/C often has less need. Activated C’s containPt/C often has less need. Activated C’s contain
absorbed oxygen.absorbed oxygen.
 Careful! The procedure involves mixing solvent,Careful! The procedure involves mixing solvent,
air, catalyst to purge residual hydrogen; recipeair, catalyst to purge residual hydrogen; recipe
for an event.for an event.

37. Noble Metals as Promoters of RaNiNoble Metals as Promoters of RaNi
 Addition of Pt, Os, Ir, or their salts had aAddition of Pt, Os, Ir, or their salts had a
dramatic effect on rate of reduction of adramatic effect on rate of reduction of a
cholesterol ketone; Rh and Ru notcholesterol ketone; Rh and Ru not
effective.effective.
 Most effective as platinic chloride;Most effective as platinic chloride;
activates for reductions of nitrile andactivates for reductions of nitrile and
alkylnitro groupsalkylnitro groups

38. Basic PromotersBasic Promoters
 Addition of KOH or NaOH to Nickel-cat.Addition of KOH or NaOH to Nickel-cat.
ketone reductions greatly increases rate.ketone reductions greatly increases rate.
Improved: reduction of nitroanilines, acylImproved: reduction of nitroanilines, acyl
phenols, phenyl phenols, alkyl phenol andphenols, phenyl phenols, alkyl phenol and
free phenols if anhydrousfree phenols if anhydrous
 Trace EtTrace Et33N added to RaNi reductions ofN added to RaNi reductions of
aldehydes and ketones cut the time inaldehydes and ketones cut the time in
half. Synergistic with platinum chloride.half. Synergistic with platinum chloride.

39. Water as a PromoterWater as a Promoter
 Addition of water most frequently improvesAddition of water most frequently improves
ruthenium reductions.ruthenium reductions.
 Ru reductions at low or moderateRu reductions at low or moderate
conditions often do not proceed withoutconditions often do not proceed without
presence of water.presence of water.
 Water counteracts effect of chloride or HClWater counteracts effect of chloride or HCl
as inhibitoras inhibitor

40. Reaction ConditionsReaction Conditions
 CatalystCatalyst
 AdjuvantAdjuvant
 SolventSolvent
 SupportSupport
 LoadingLoading
 TemperatureTemperature
 PressurePressure
 Method of agitationMethod of agitation

41. SolventSolvent
 Hydrogenations can be run sans solvent.Hydrogenations can be run sans solvent.
 Solvents moderate reactions and exothermsSolvents moderate reactions and exotherms
 SM does not need to be dissolved or even beSM does not need to be dissolved or even be
significantly soluble, so long as product is.significantly soluble, so long as product is.
 Effect of solvent choice is reaction-specific.Effect of solvent choice is reaction-specific.
 Acidic and basic solvents serve a dual purpose.Acidic and basic solvents serve a dual purpose.
 The effect of a neutral solvent is unpredictable.The effect of a neutral solvent is unpredictable.

42. Solvents continuedSolvents continued
 The neoprene stopper of Parr Shakers isThe neoprene stopper of Parr Shakers is
attacked by ketones, ethyl acetate,attacked by ketones, ethyl acetate,
benzene, THF and pyridine, but is inert tobenzene, THF and pyridine, but is inert to
alcohols, water, alkane solvents. Solventalcohols, water, alkane solvents. Solvent
choice may require sacrificing stopper orchoice may require sacrificing stopper or
using alternate closure.using alternate closure.
 High pressure autoclaves are consistentHigh pressure autoclaves are consistent
with any organic solventwith any organic solvent but not mineralbut not mineral
acids.acids.

43. Solvents continuedSolvents continued
 Common Solvent Choices:Common Solvent Choices:

WaterWater

methyl and ethyl alcoholmethyl and ethyl alcohol

Ethyl acetate, cyclohexane,Ethyl acetate, cyclohexane,
methylcyclohexane, benzene, pet ether,methylcyclohexane, benzene, pet ether,
ligroinligroin
 Methyl cellosolve (MeOCHMethyl cellosolve (MeOCH22CHCH22OH)OH)

DMFDMF

Acetone, MEKAcetone, MEK

44. Solvents continuedSolvents continued
 Solvents are not always inert:Solvents are not always inert:

Reduction of pyridine over nickel in lower alkylReduction of pyridine over nickel in lower alkyl
solvents results in N-alkylationsolvents results in N-alkylation

Reductions in THF and dioxane at high tempsReductions in THF and dioxane at high temps
over nickel make explosive mixtures. Soover nickel make explosive mixtures. So

DIOXANE AND THF ARE FORBIDDENDIOXANE AND THF ARE FORBIDDEN
IN THE HIGH PRESSURE LAB!IN THE HIGH PRESSURE LAB!

45. SupportSupport
 Used to increase surface area of catalystUsed to increase surface area of catalyst
with consequent higher rateswith consequent higher rates
 Modifies SelectivityModifies Selectivity
 (Process) Minimizes loss of catalyst(Process) Minimizes loss of catalyst

46. Common SupportsCommon Supports
 Carbon (many variations): high surfaceCarbon (many variations): high surface
area, absorbs oxygen and impurities; mostarea, absorbs oxygen and impurities; most
common and reliable.common and reliable.
 Alumina: Absorbs impurities. pH ofAlumina: Absorbs impurities. pH of
Alumina can modulate selectivity.Alumina can modulate selectivity.
 Alkaline earth carbonates: impart basicityAlkaline earth carbonates: impart basicity
(in some cases impedes polymerization of(in some cases impedes polymerization of
alkynes).alkynes).

47. SupportsSupports
 There are many types of support designedThere are many types of support designed
for specific reductions and situations,for specific reductions and situations,
includingincluding
 ClaysClays
 CeramicsCeramics
 PumicePumice
 CeliteCelite

48. Catalyst LoadingCatalyst Loading
 Rate is semi-proportional to catalystRate is semi-proportional to catalyst
loadingloading but not linearbut not linear. (Low loading may. (Low loading may
give no reaction at all, but doubling atgive no reaction at all, but doubling at
midrange may give 5-20x effect).midrange may give 5-20x effect).
 Use and report loading based upon weightUse and report loading based upon weight
percent of total catalyst (not containedpercent of total catalyst (not contained
metal)vs substrate.metal)vs substrate.
 Scale-ups require a smaller loading thanScale-ups require a smaller loading than
pilots.pilots.

50. TemperatureTemperature
 Classic rate vs temperature rules applyClassic rate vs temperature rules apply
 Lower temperatures are preferable, asLower temperatures are preferable, as
they exaggerate selectivity differences.they exaggerate selectivity differences.
 Many reductions are exothermic; useMany reductions are exothermic; use
more solvent, less agitation, or lessmore solvent, less agitation, or less
hydrogen pressure to moderatehydrogen pressure to moderate
 Parr limit: 80Parr limit: 80°C HP autoclave: 300 °C°C HP autoclave: 300 °C

51. AgitationAgitation
 Shaking (Parr Shaker) Efficient for smallShaking (Parr Shaker) Efficient for small
quantities, but difficult to achieve over 2 L.quantities, but difficult to achieve over 2 L.
 Rocking (Rocker autoclaves) Less efficientRocking (Rocker autoclaves) Less efficient
than rocking or stirring, but best choice forthan rocking or stirring, but best choice for
high pressures.high pressures.
 Stirring: Depending upon design, can beStirring: Depending upon design, can be
very efficient. Magnetically coupled shaftsvery efficient. Magnetically coupled shafts
permit much more reliable performance.permit much more reliable performance.
 Extensive discussion in AugustineExtensive discussion in Augustine

52. Agitation continuedAgitation continued
 Rate of reaction increases with efficiencyRate of reaction increases with efficiency
of stirring (e.g. mixing of phases)of stirring (e.g. mixing of phases)
 Magnetically stirred microhydrogenatorsMagnetically stirred microhydrogenators
become ineffective above 50 mL.become ineffective above 50 mL.
 Why?Why?

53. Two Standard MixersTwo Standard Mixers

54. PressurePressure
 A great many Pt and Pd reductions can beA great many Pt and Pd reductions can be
achieved at 60 psi with proper choice of solventachieved at 60 psi with proper choice of solvent
and promotersand promoters
 Rate is (nonlinearly) proportional to pressure.Rate is (nonlinearly) proportional to pressure.
 Some catalysts (Cobalt, copper arsenite) requireSome catalysts (Cobalt, copper arsenite) require
higher pressures (up to 200 atm) to perform.higher pressures (up to 200 atm) to perform.
Some substrates such as aromatics areSome substrates such as aromatics are
resistant to hydrogenation and require highresistant to hydrogenation and require high
pressurepressure

55. Atmospheric HydrogenatorAtmospheric Hydrogenator

56. End of HydrogenationEnd of Hydrogenation
Part OnePart One