experiment 24: synthesis and gc analysis of fatty acid methyl esters
TRANSCRIPT
Experiment 24:
SYNTHESIS AND GC ANALYSIS OF FATTY ACID METHYL ESTERS
CH2O
CHO
C
O
R
C
O
R'
CH2O C
O
R"
KOHCH3OH
CH2OH
CHOH
CH2OH
+
RCO2CH3
R'CO2CH3
R"CO2CH3
Vegetable oil
Glycerol Fatty acid methyl esters(FAMES)forms CH3O-K+
and H2O
Objectives:
To synthesize fatty acid methyl esters through transesterification of an unknown vegetable oil.
To purify your product using column chromatography.
To identify and analyze the purity of your compound using TLC and GC analysis.
To identify the unknown oil based on fatty acid methyl ester composition.
CHEMICAL EQUATION(Hydrolysis of a fat)
CH2O
CHO
C
O
R
C
O
R'
CH2O C
O
R"
-OH
CH2OH
CHOH
CH2OH
+
fat
Glycerol
CR
O
O
CR'
O
O
CR"
O
O
Fatty Acid salts
H3O
CR
O
OH
CR'
O
OH
CR"
O
OH
Fatty Acids
CHEMICAL EQUATION(Transesterification of vegetable oil)
CH2O
CHO
C
O
R
C
O
R'
CH2O C
O
R"
KOHCH3OH
CH2OH
CHOH
CH2OH
+
Vegetable oil
Glycerol
Fatty acid methyl esters(FAMES)
forms CH3O-K+
and H2O
CR
O
O CH3
CR'
O
O CH3
CR"
O
O CH3
COMMON FATTY ACIDS
OH
O
Linoleic Acid (polyunsaturated) 18:2 9,12
18
12
9
O
OH14 Myristic Acid (saturated)
14:0O
OH
Palmitic Acid (saturated) 16:0
16
O
OH
Stearic Acid (saturated) 18:0
18
OH
O
Oleic Acid (monounsaturated) 18:1 9
18
9
Saturated= NO double bonds!
Monounsaturated= ONE double bond!
Polyunsaturated= >one double bond!
SHAPES OF FATTY ACIDS
More cis double bonds = more “bent” shape
EXPERIMENTAL PROCEDURE
(Synthesis)
Add 10 drops of unknown oil and methanol to a reaction vial with stir bar.
Add 1M KOH/methanol. Place vial in heat block and
begin stirring the solution. Attach reflux condenser. Heat to reflux. *Maintain
temperature b/n 70-80oC for 30 minutes.* (Excessive heat will ruin experiment!)
Cool flask to room temp.
EXPERIMENTAL PROCEDURE
(Purification and Isolation)
Extract product 2X with hexane 1X with 9:1 hexane: diethyl
ether.
After each extraction step, pass organic layer through SiO2 column into a small test tube.
Proceed to PRODUCT ANALYSIS.
EXPERIMENTAL PROCEDURE
(Product Analysis)
TLC Analysis Perform analysis of product along with provided
standards of the unknown oil and FAMEs solutions.
Must use 10% H2SO4 stain with heat in order to visualize spots.
Have stained TLC plate inspected by lab instructor to ensure polar impurities have been completely removed.
GC Analysis With instructor permission, prepare sample for
GC analysis.
GC ANALYSIS OF FAMES STANDARD SOLUTION
• Once returned, identify and quantify FAMEs present in your unknown oil.
• Compare these results to table on p. 203 in order to identify your unknown oil.
Table 24.1
Be sure to give CENTIMETER measurements for ALL spots and give measurement for SOLVENT FRONT on this diagram!
Table 24.2
Compound GC Retention Times
(min)Area Perce
nt
Adjusted
Area %Standard
Sample
pentaneXXX
Methyl Palmitate
Methyl Oleate
Methyl Linolate
Methyl Stearate
RELATIVE COMPOSITION OF OILS
Name of Oil
Saturated Fatty Acids
Total % SFUs
Monounsaturated
Fatty Acids
Polyunsaturated
Fatty Acids Total % PUFAs
MyristicC14
(14:0)
PalmiticC16
(16:0)
StearicC18
(18:0)
OleicC18
(18:19)
Linoleic C18
(18:19,12)
Corn 0 11 2 13 28 58 59
Olive 0 13 3 16 71 10 11
Peanut 0 11 2 13 48 32 32
Soybean 0 11 4 15 24 54 61
Safflower 0 7 2 9 13 78 78
Cottonseed
1 22 3 26 19 54 55
Palm 1 45 4 50 40 10 10
Table 24.3
Unknown LetterDid you use UNKNOWN A, B, or C?
% SFA Once you have a tentative identification of your unknown vegetable oil based on your comparison of the calculated values in Table 24.2 to the table on p. 201 of your lab manual, complete this table by filling in the EXPECTED % for your oil using the values provided in the table on p. 203.These values may not match your calculated values EXACTLY, but should be close enough for you to have verification of the identity of your unknown oil!
%MUFA
%PUFA
Unknown IdentityGive the name of your unknown oil
here!
SAFETY CONCERNS
CAUTION: SULFURIC ACID and POTASSIUM HYDROXIDE are very corrosive! HEXANE and DIETHYL ETHER are extremely flammable!
METHANOL is very flammable and toxic!
WASTE MANAGEMENT
• All liquid waste in container labeled “ORGANIC WASTE (FAMEs).
• Leave TLC plates with instructor.
• Place filter papers in the yellow SOLID WASTE can.
• Place used TLC capillaries, SiO2 columns, and glass Pasteur pipets in broken glass container.
CLEANING
Rinse all glassware with wash acetone ONLY!
DO NOT return any glassware to lab drawer dirty or wet!