Term
| Catalytic hydrogenation can be divided into two categories: |
|
Definition
| heterogeneous and homogeneous |
|
|
Term
| Hetereogenous catalyst: Noble metal catalyst and supported |
|
Definition
| -Pt, Pd, Ru, Rh, Os (supported on C, BaSO4, CaSO4) |
|
|
Term
Activity of catalyst support
BaSO4
CaSO4
C |
|
Definition
|
|
Term
| What pressure and temperature should you be at for catalytic hydrogenation with heterogenous catalysts |
|
Definition
| 1-4 atm pressure, temperature r.t. to high temps |
|
|
Term
|
Definition
| finely grained solid mostly of nickel (ca. 89%) derived from Ni-Al alloy |
|
|
Term
| What are active grades of Raney Nickel? |
|
Definition
| lower temperatures and pressures because H2 has already absorbed |
|
|
Term
| What are less active grades of Raney Nickel? |
|
Definition
| HIGH TEMPERATURES (R.T.-->300c) and high pressure (100-300 atm) |
|
|
Term
Reactivity of catalyst
Pd, CuCr2O3, RaNi, active RaNi, Pt, Ru,Rh |
|
Definition
| Pt>Pd>Active RaNi>Ru Rh> RaNi> CuCr2O4 |
|
|
Term
| What is the role of Pb and Quinoline when using lindlar's catalyst? |
|
Definition
pb deactivates the palladium sites
quinoline offers further deactivation and selectivity enhancement |
|
|
Term
| Selectivity of alkene hydrogenaton |
|
Definition
|
|
Term
| Addition in syn can be altered by |
|
Definition
| using less active catalyst, acidity, solvent polarity, direction groups |
|
|
Term
Bond migration and stereochemistry:
more probable with ___
positional isomers and ___/____ isomers
__ also causes similar problems but less likely |
|
Definition
|
|
Term
| Ketones and aldehydes: heterogenous catalyst for reduction reactivity |
|
Definition
| acyl chloride> R-NO2> alkene> alkyne> aldehyde> cyano> ketone (typically active rani or PtO2)>>>esteres>>>amides |
|
|
Term
| Auwers-Skita rules are related to |
|
Definition
| physicals properties of geometrical isomer and their configurations and is used for a guide for stereochemical course of H2 with C=O in cyclic ketones in different solvents |
|
|
Term
| Auwers-Skita rule in acidic condition, |
|
Definition
| reduction is rapid and general from less-hindered base of C=O giving axial alcohol (kinetic control) |
|
|
Term
| Auwers-Skita rule in basic or neutral condition, ` |
|
Definition
| gives equatorial alcohol, if ketone is not hindered (thermodynamic contraol) in strongly hindered ketones, reaction will give axial alcohol again |
|
|
Term
| Why are homogeneous catalysts preferred? and examples? |
|
Definition
preferred since less variable in activity
Rh, Ru, Ir, etc. wilkinson catalyst |
|
|
Term
| Homogenous catalysts: selectivity for NO2 |
|
Definition
NO2 are very less prone,
reduces alkenes and alkynes in presence of CO, CN, N3, S, NO2, Cl |
|
|
Term
| Dissolving metal reductions Group 1 (Li, Na, K, Ca) things to know |
|
Definition
used in solutions of liquid NH3
with or witout cosolvent and proton donor
sometimes volatile alkylamines instead of NH3
will reduce many multiple double bonds and cleave many disruptable sigma bonds, generally between carbon and heteroatom |
|
|
Term
| Dissolving metal reductions Group 2 (Na-amalgam, Zn, Mg, Sn, Fe) |
|
Definition
often used in hydroxylic solvents (ROH, water)
often under acidic conditons |
|
|
Term
| Multiple bonds specific reductions preformed with group 1 and 2 metals |
|
Definition
isolated C=C generally resistant
conjugated C=C much more susceptible because of stabilzation of radical
thermodynamic product |
|
|
Term
Rank these reducing agents
LiBH4
LiAlH4
NaBH4
NaBH3Cn |
|
Definition
| LiAlH4>LiBH4>NaBH4>NaBH3CN |
|
|
Term
|
Definition
| ketones, aldehydes, esters, alkylhalides, acyl halides, amide, epoxides, nitriles |
|
|
Term
|
Definition
| ketones, aldehydes, esters |
|
|
Term
|
Definition
|
|
Term
| What does NaBH3CN reduce? |
|
Definition
|
|
Term
| 3 things to look at to compare reducing reagents |
|
Definition
cation
electronegativity
hydride becomes less stable |
|
|
Term
|
Definition
| Li is a better lewis acid than sodium which increases electrophilicity of the carbon |
|
|
Term
|
Definition
| more EN atom will provide less electron density to hydrides, thus is less nucleophilic |
|
|
Term
| Hydride becomes less stable: |
|
Definition
| as we go down the groups; (HM gets weaker so easier to get off) |
|
|
Term
|
Definition
| is much more reactive than NaBH4 but selective than LAH |
|
|
Term
| What do BH3*THF rapidly reduce and not reduce |
|
Definition
aldehydes, ketones lactones, COOH, tertiary amines
NOT acyl chlorides, esters, carboxylate salts and nitro groups |
|
|
