5 FA distribution

Question 1

what is hydrogenation and what are its applications?

Answer 1

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

Question 2

what is an IV?

Answer 2

iodine value; GRAMS of iodine absorbed by 100 g of fat.

Question 3

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?

Answer 3

direct; higher

Question 4

what ratio does I2 react with an unsaturated fat?

Answer 4

1:1 per double bond

Question 5

what is selectivity?

Answer 5

the preference for hydrogenation to occur to more more highly unsaturated FAs

Question 6

what are the factors that influence hydrogenation reaction rate?

Answer 6

• degree of unsaturation
• nature and concentration of catalyst
• rxn presure [H]
• temp
• degree of agitation

Question 7

what are the steps of hydrogenation

Answer 7

1) transfer/diffusion
2) adsorption
3) hydrogenation/isomerization
4) desorption
5) transfer

Question 8

what happens during the transfer/diffusion step of hydrogenation?

Answer 8

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

Question 9

would oleic or linoleic acid be selectively preferred during hydrogenation?

Answer 9

linoleic

Question 10

how is selectively expressed as?

Answer 10

Kln/Ko = rate of hydrogenation of linoleate relative to oleate

Question 11

what is copper (CuO + Cr2O3) catalyst selective for?

Answer 11

linoleate. Kln/Ko=10

Question 12

how is catalyst activity defined by the American Oil Chemist’s Society?

Answer 12

IV decrease per unit of time during a hydrogenation under a specific set of conditions

Question 13

what are the conditions for determining catalyst activity of soybean oil?

Answer 13

IV: 120 to 80
temp: 350°F
pressure: 20 psig
[catalyst]: 0.05%

Question 14

what is catalyst lifetime?

Answer 14

how long a catalyst remains active/useful

Question 15

is hydrogenation stereoselective?

Answer 15

no, locations aren’t being altered.

Question 16

what are the independent variables that influence the rate of hydrogenation?

Answer 16

• temp
• pressure
• agitation
• catalyst concentration

Question 17

what are the dependent variables that influence hydrogenation?

Answer 17

• nature of FA (trans FAs)
• nature of catalyst (selectivity ratio)
• hydrogenation rate

Question 18

as temp increases, the selectivity ratio:

Answer 18

increases

Question 19

as temp increases, the trans content:

Answer 19

increases

Question 20

as temp increases, the reaction rate:

Answer 20

increases

Question 21

as pressure increases, the selectivity ratio:

Answer 21

decreases

Question 22

as pressure increases, the trans content:

Answer 22

decreases

Question 23

as pressure increases, the reaction rate:

Answer 23

increases

Question 24

as agitation increases, the selectivity ratio:

Answer 24

decreases

Question 25

as agitation increases, the trans content:

Answer 25

decreases

Question 26

as agitation increases, the reaction rate:

Answer 26

increases

Question 27

as catalyst concentration increases, the selectivity ratio:

Answer 27

increases

Question 28

as catalyst concentration increases, the trans content:

Answer 28

increases

Question 29

as catalyst concentration increases, the reaction rate:

Answer 29

increases

Question 30

what are the only independent variables in hydrogenation that have in indirect relationship with selectivity ratio and trans content?

Answer 30

pressure and agitation

Question 31

what are the methods used to analyze modified TGs?

Answer 31

• IV
• saponification value
• Gas Chromatography (GC) for FAs
• Liquid Chromatography

Question 32

define saponification

Answer 32

hydrolysis of ester under alkaline conditions

Question 33

what is the saponification value?

Answer 33

number of mg of KOH required to completely hydrolyze/neutralize 1 g of sample

Question 34

how do you calculate the saponification value?

Answer 34

(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

Question 35

what acid and color indicator are used for saponification?

Answer 35

HCl, phenolphthalein

Question 36

how many moles of KOH does a TG, DG, and MG respectively require to be fully hydrolyzed?

Answer 36

3, 2, 1

Question 37

if your TG is 1 g, how many g of KOH do you need to fully hydrolyze it?

Answer 37

168,000/(molecular weight of TG)

OR

168,000/(average molecular weight of TG)

Question 38

how do you calculate the AVERAGE molecular weight of a SIMPLE TG?

Answer 38

41 + 3 x (MWfar-1)

Question 39

how do you calculate the AVERAGE molecular weight for a MIXED TG?

Answer 39

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)

Question 40

what are the 6 steps for GC analysis of FAs?

Answer 40

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

Question 41

how are FAs identified using GC?

Answer 41

each FA has a unique retention time

Question 42

what reactions are involved with Wij’s method for determining IV?

Answer 42

R-CH=CH-R + 2 ICl –> R-ICH-ICH-R + 2HCl
ICl + KI –> KCl + I2
Na2S2O3 + I2 –> 2 NaI + Na2S4O6