5 FA distribution Flashcards
what is hydrogenation and what are its applications?
addition of H2 in the presence of a catalyst to reduce level of unsaturation or convert cis/trans bonds; can make more plastic fats from oils
what is an IV?
iodine value; GRAMS of iodine absorbed by 100 g of fat.
degree of UNsaturation and IV have an direct or indirect relationship? therefore, a fat with a higher degree of unsaturation would have a (higher/lower) IV?
direct; higher
what ratio does I2 react with an unsaturated fat?
1:1 per double bond
what is selectivity?
the preference for hydrogenation to occur to more more highly unsaturated FAs
what are the factors that influence hydrogenation reaction rate?
- degree of unsaturation
- nature and concentration of catalyst
- rxn presure [H]
- temp
- degree of agitation
what are the steps of hydrogenation
1) transfer/diffusion
2) adsorption
3) hydrogenation/isomerization
4) desorption
5) transfer
what happens during the transfer/diffusion step of hydrogenation?
CRITICAL STEPS. controls degree of isomerization and selectivity
transfer: take reactants/products to and from liquid phase and surface of catalyst
diffusion: diffusion of reactant into pores/product out of pores of the catalyst
would oleic or linoleic acid be selectively preferred during hydrogenation?
linoleic
how is selectively expressed as?
Kln/Ko = rate of hydrogenation of linoleate relative to oleate
what is copper (CuO + Cr2O3) catalyst selective for?
linoleate. Kln/Ko=10
how is catalyst activity defined by the American Oil Chemist’s Society?
IV decrease per unit of time during a hydrogenation under a specific set of conditions
what are the conditions for determining catalyst activity of soybean oil?
IV: 120 to 80
temp: 350°F
pressure: 20 psig
[catalyst]: 0.05%
what is catalyst lifetime?
how long a catalyst remains active/useful
is hydrogenation stereoselective?
no, locations aren’t being altered.
what are the independent variables that influence the rate of hydrogenation?
- temp
- pressure
- agitation
- catalyst concentration
what are the dependent variables that influence hydrogenation?
- nature of FA (trans FAs)
- nature of catalyst (selectivity ratio)
- hydrogenation rate
as temp increases, the selectivity ratio:
increases
as temp increases, the trans content:
increases
as temp increases, the reaction rate:
increases
as pressure increases, the selectivity ratio:
decreases
as pressure increases, the trans content:
decreases
as pressure increases, the reaction rate:
increases
as agitation increases, the selectivity ratio:
decreases
as agitation increases, the trans content:
decreases
as agitation increases, the reaction rate:
increases
as catalyst concentration increases, the selectivity ratio:
increases
as catalyst concentration increases, the trans content:
increases
as catalyst concentration increases, the reaction rate:
increases
what are the only independent variables in hydrogenation that have in indirect relationship with selectivity ratio and trans content?
pressure and agitation
what are the methods used to analyze modified TGs?
- IV
- saponification value
- Gas Chromatography (GC) for FAs
- Liquid Chromatography
define saponification
hydrolysis of ester under alkaline conditions
what is the saponification value?
number of mg of KOH required to completely hydrolyze/neutralize 1 g of sample
how do you calculate the saponification value?
(56.1(g/mol) x (B-S) x HCL normality)/g sample
B = volume of HCL to reach BLANK endpoint S = volume of HCL to reach SAMPLE endpoint
what acid and color indicator are used for saponification?
HCl, phenolphthalein
how many moles of KOH does a TG, DG, and MG respectively require to be fully hydrolyzed?
3, 2, 1
if your TG is 1 g, how many g of KOH do you need to fully hydrolyze it?
168,000/(molecular weight of TG)
OR
168,000/(average molecular weight of TG)
how do you calculate the AVERAGE molecular weight of a SIMPLE TG?
41 + 3 x (MWfar-1)
how do you calculate the AVERAGE molecular weight for a MIXED TG?
same as simple but this time you sum the mw of each the different FAs (you might have 2 of one FA or all three are different)
what are the 6 steps for GC analysis of FAs?
1) extract
2) saponify
3) prepare methyl esters
4) chromatograph methyl esters (CH3ONa)
5) determine peak areas of FAs
6) compare with response curve of standards
how are FAs identified using GC?
each FA has a unique retention time
what reactions are involved with Wij’s method for determining IV?
R-CH=CH-R + 2 ICl –> R-ICH-ICH-R + 2HCl
ICl + KI –> KCl + I2
Na2S2O3 + I2 –> 2 NaI + Na2S4O6
