4. Interesterification + Hydrogenation + Winterization Flashcards
Interesterification vs intraesterification
- Inter: exchange of acyl groups among TG molecules
- Intra: acyl groups may also exchange position within a TG molecule
What characteristic (2) regarding FA position do you want in an oil after transesterification?
low GS3 and GS2U
3 step reaction mechanism for transesterification
- formation of enolate ion
- formation of beta-keto ester
- interesterification
What are the catalysts for interesterification?
- high temp vs low temp
- strong bases! usually
- high temp: KOH and NaOH –> KOH is favored bc weaker base, you don’t want to saponify
- low temp: sodium methoxide (NaOCH3) (weaker base)
how it an enolate ion formed? stable?
initial removal of proton from carbon adjacent to acyl group (alpha carbon) by the base catalyst –> leads to charge delocalized enolate anion
- anion is very unstable –> resonance to stabilize (negative charge shared between O and alpha carbon)
Random vs directed interesterification
- random: when interesterification carried out to equilibrium condition –> FA assume almost random distribution among TG
- directed: interesterification can be directed away from its usually random end-point if fat is allowed to crystallize during reactions (trisaturated glycerides crystallize first)
Lard interesterification:
- Crystal modified lard (CML)?
- Partially modified lard (PML)?
- Direct interesterified lard (DIL)
- CML: conditions favors intramolecular interchange
- PML: conditions favoring random distribution
- DIL: conditions favoring directed interesterification to control the GS3 content –> = highest unsat!
enzyme catalyzed interesterification in presence of water also used for manufacture of ________&________, extensively used by food industry as _____________
- mono and diglycerides
- emulsifiers
what is simple way to obtain glycerol and FFA?
- add NaOH to TG and boil
Hydrogenation super important to eliminate ?????
reliance on butter
-2 main purposes of catalytic hydrogenation?
+ Why is catalytic hydrogenation a very important reaction in organic synthesis? give example
- convert oil to fat (remove double bond)
- reduce susceptibility of oil to oxidative rancidity
in certain cases, isomerization of double bond is the desired outcome (ie pharmaceutical industry)
how is catalyst used in hydrogenation? 2 steps
- oil + catalyst –> oil-catalyst complex
- oil catalyst complex + H2 –> hydrogenated oil + catalyst
how is catalyst activity of hydrogenation defined?
- defined as decrease in iodine number per unit of time during a hydrogenation under specific set of conditions
iodine value defined as?
- what does it indicate?
number of grams of iodine (I2) absorbed by 100g of fat
- unsat FA residues react with iodine –> iodine number indicates degree of saturation of FA residues of glyceride
high degree of unsaturation = (high or low) iodine value
High!
how does I2 docks onto double bond?
1 I goes to each carbon = no double bond anymore
Iodine value of tristearin?
0!
if 0.01 moles of linoleic acid reacts with 5.1g of iodine. determine number of double bonds present in FA. Assuming 1 mol of iodine = 254g.
5.1g of iodine = 0.02 mol I2
0.01 mol linoleic acid = 0.01 mol I2
2 double bonds!
Calculate iodine number of linoleic acid C17H31COOH
181!
trans FA have higher or lower melting point that cis isomer?
higher!
Selectivity in hydrogenation? refers to?
- how can you vary selectivity?
- selectivity useful today?
refers to preferentially hydrogenating more highly unsaturated FA
- by varying catalysts/operating conditions
- Not in food industry! but useful in pharma
5 factors that affect reaction rate of hydrogenation
- nature of substance fo be hydrogenated
- nature and concentration of catalyst
- reaction pressure (ie concentration of hydrogen)
- reaction temperature
- degree of agitation (mix catalyst in solution)
5 steps in hydrogenation of oils
- which are critical steps in controlling degree of isomerization and selectivity of reactions?
- transfer and/or diffusion
- absorption
- hydrogenation/isomerization
- desorption
- transfer
- transfer/diffusion and absorption!
transfer vs diffusion
- transfer: transfer of reactants and products to and from the bulk of the liquid oil phase and outside surface of catalyst
- diffusion: diffusion of reactant into pores of the catalyst + diffusion of products out of the pores of catalysts
