Myristic Acid Synthesis

Question 1

What are the two main reactions performed when synthesizing myristic acid?

Answer 1

1) Ester hydrolysis (ester as the hydrolyzer)

2) Neutralization (to get the myristic acid) (protonation)

Question 2

What is myristic acid also known as?

Answer 2

TRI-ESTER

–> It’s a molecule that contains 3 ester linkages to 3 long carbon chains

Question 3

What is the hydrolysis reaction of trimyristin?

Answer 3

Trimyristin + KOH (potassium hydroxide) + heat

= Potassium Myristae (a carboxylate salt) + Glycerol

Question 4

When esters are treated with hydroxides…

Answer 4

They are HYDROLYZED to form carboxylic acids (single bonded O gains an H to form a COOH group)

BUT hydroxide creates basic environment so the carboxylic acid is rapidly reacted to form carboxylate salts (H is removed from OH and O gains a negative charge)

Question 5

Why must the potassium myristate be neutralized?

Answer 5

Because it is negatively charged (basic) and so to form myristic acid it must be neutralized (protonated) to get it to a zero charge state with an H added to form myristic acid

Question 6

How is potassium myristate neutralized?

Answer 6

Potassium myristae is reacted with HYDROGEN CHLORIDE (HCl) to protonate the compound and form myristic acid

Question 7

What is the ratio of trimyristin hydrolyzed to potassium myristate produced?

Answer 7

1:3

For every one trimyristin molecule that is hydrolyzed, THREE potassium myristate molecules are formed

(As hydrolysis breaks the bonds at each ester linkage)

Question 8

What is potassium myristate in relation to myristic acid?

Answer 8

Myristate is the conjugate base of myristic acid

Question 9

Why don’t you get myristic acid after hydrolysis?

Answer 9

Because the reaction is conducted under basic conditions and so the myristic acid formed from hydrolysis reacts with the basic environment and get deprotonated immediately to form myristate instead

Question 10

A procedure for the ester hydrolysis experiment calls for using 0.2 mmol trimyristin and 4.5 mmol KOH. How many millimoles (mmol) of myristic acid can be prepared following this protocol?

A. 4.5 mmol
B. 0.2 mmol
C. 2.25 mmol
D. 0.4 mmol
E. 0.6 mmol
F. 1.0 mmol

Answer 10

E. 0.6 mmol

1) We know that there is excess amount of KOH (4.5 mmol) and so all of the trimyristin WILL react and undergo hydrolysis

–> Meaning 0.2mmol of trimyristin will undergo hydrolysis

2) Remember the ratio of trimyristin to myristic acid formation is 1:3

–> Therefore the amount of myristic acid that could theoretically be produced is (0.2)(3) = (0.6mmol)

Question 11

Reflux

Answer 11

A method utilized to heat substances at a constant temperature while maintaining a constant volume (no loss of liquid to environment)

Constant temperature baths are used to ensure uniform, reproducible rxn conditions

Question 12

Reflux Setup

Answer 12

1) Variac plugged into heating mantle

2) Heating mantle clamped to ring stand ABOVE the bench (floating)

3) RBF sitting in heating mantle; also CLAMPED to the ring stand at its neck

4) Condenser inserted into the RBF; also CLAMPED to the ring stand
a) Ground glass joint should be greased

5) Thin walled hosing connected to condenser
a) Bottom outlet = water input –> Connected to faucet
b) Top outlet = water output –> Connected to drain

Question 13

Variac

Answer 13

Transformer that controls the amount of heat output of the heating mantle

Question 14

What is the direction of water flow through a condenser?

Answer 14

Water goes in from the bottom and out from the top

Question 15

Why is reflux utilized to heat substances?

Answer 15

Reflux uses a condenser to keep a steady reaction volume in an open system despite heating

Question 16

What is the overall purpose of the condenser in reflux?

Answer 16

To prevent evaporation of solvent!

To re-condense any vapors from heating that will then go back into the RBF

–> Prevents loss of substance to evaporation! (keeps it contained and at a steady volume)

Question 17

Why must the heating mantle be raised?

Answer 17

The heating mantle is raised so that in case a reaction gets out of control, you can quickly drop the mantle from the RBF with the sample

–> Allows for immediate removal of the heat source

Question 18

What is the purpose of a boiling stone?

Answer 18

Ensures even boiling of a substance

Question 19

Why is the water input at the bottom of a condenser?

Answer 19

Because when vapor rises you want it to condense as soon as possible so having the coldest water (from the faucet) at the lowest point in the condenser (near the RBF neck) allows condensation to happen faster

Question 20

When does the timer for reflux begin (reflux start point)?

Answer 20

When the first drop of condensed liquid returning to the RBF is observed

(reflux goes for 1 hour)

Question 21

Once reflux time is complete (1 hour) what is the first thing you should do?

Answer 21

Drop the heating mantle

THEN turn it off

Question 22

What, if observed during reflux, should make you drop the heating mantle?

Answer 22

If vapor is rising up to more than 1/4 of the way up the condenser, DROP THE MANTLE

Question 23

After reflux, what do we have in the RBF?

Answer 23

Potassium myristate (in basic conditions)

Question 24

The reaction between an acid and a base favors which side of the reaction?

Answer 24

Favors the direction of reaction that will produce acids/bases WEAKER than the reactants!

Question 25

If the pKa of the reactant acid is higher than the pKa of the product acid, which direction will be favored in the reaction?

Answer 25

The REVERSE reaction!

Higher pKa = weaker acid

therefore, the reactant acid is weaker than the product acid so the forwards direction would NOT be favored!

Question 26

Acidification process for myristate

Answer 26

1) Pour the reflux rxn mixture (containing myristate) into cold HCL

2) Mix thoroughly to allow for protonation of all the myristate

3) Test pH to ensure successful acidification

Question 27

Once the myristate has been acidified, how do we collect the myristic acid from the solution? WHY?

Answer 27

By combining the acidic mixture with WATER and then using VACUUM FILTRATION

Myristate is CHARGED and so it is SOLUBLE in water

Myristic Acid is NOT CHARGED and so it is actually INSOLUBLE in water!!!

–> Therefore myristic acid will precipitate out of solution upon the addition of water which we will collect with vacuum filtration

Question 28

Once myristic acid is extracted, why must it be purified?

Answer 28

Myristic acid must be purified because in water, the micelles formed are most likely contaminated

When myristic acid aggregates to form a micelle, one or a few myristates may get aggregated along with them, contaminating the micelle

Question 29

Amphiphilic

Answer 29

Chemical compound possessing both hydrophilic and lipophilic properties

Question 30

What occurs to amphiphillic molecules in water?

Answer 30

They form MICELLES

–> Molecular AGGREGATES in a circular arrangement in which POLAR heads are exposed to the water and NON-POLAR ends are kept away from the water

Question 31

Myristic acid and myristate are what kind of molecules?

Therefore what happens to them in water?

Answer 31

Amphiphilic molecules (both contain a polar and non-polar end)

Polar Ends:
–> Myristic Acid = OH end
–> Myristate = O (-) end

Question 32

How do we purify the myristic acid (from the myristate)?

Why?

Answer 32

We dissolve the extracted (impure) myristic acid in LIGROIN

Ligroin is an organic compound in which the solubility of myristic acid and myristate differ!

Myristic acid = DISSOLVES in ligroin
Myristate = INSOLUBLE in ligroin (due to the - charge)

Question 33

What happens to the myristic acid micelle when dissolved in ligroin?

Answer 33

The myristic acid components of the micelle break from the micelle and dissolve in the ligroin

This leaves the myristate as insoluble particles in the ligroin

Question 34

Once dissolved in ligroin, how is the dissolved myristic acid separated from the precipitated myristate?

Answer 34

Through COLUMN FILTRATION

–> Utilizes celite (clay) which is known to trap soap particles (myristate) but allowing other substances to pass through (like the myristic acid!)

Question 35

Components of the column filtration apparatus

Answer 35

1) Pipette with piece of cotton rolled towards its tip

2) Celite placed ontop of the cotton

3) Column placed into collection test tube

Question 36

Upon column filtration where do the myristate and myristic acid end up?

Answer 36

Myristate ends up stuck in the CELITE

Myristic acid flows through the celite and thus flows through the column and into the collection tube

Question 37

What is the purpose of adding norit to the crude myristic acid solution (w/ ligroin and contaminant myristate)?

Answer 37

To decolor the myristic acid (the lab gave us colorized myristic acid so we couldn’t cheat)

Question 38

Upon mixture of the ligroin to the collected (impure) myristic acid, what may you observe?

Answer 38

The formation of two liquid phases

Question 39

Why may two phases form once ligroin is added to the extracted myristic acid?

Answer 39

Because if the myristic acid is still wet with water from the vacuum filtration, the water and ligroin DO NOT mix!

They are immiscible liquids and so two phases may form

Question 40

If two phases are observed in the test tube with the myristic acid and ligroin, which phase are you supposed to collect?

Answer 40

The TOP/UPPER phase –> Contains the ligroin

Question 41

Pure piperazine has a m.p. of 106 C. Pure resorcinol has a m.p. of 110 C. A 1:1 mixture of piperazine and resorcinol is expected to have a m.p. of:

A. Less than 106 C.
B. 106 C
C. 108 C
D. 110 C
E. Greater than 110 C

Answer 41

A. Less than 106 C.

REMEMBER: Upon the mixture of two substances (impure species), the melting point DEPRESSES

Therefore, the melting point will depress to be lower than the MP of the substance with the lower MP!

Question 42

Why did we compare the melting point of the following?

1) Myristic acid
2) Trimyristin
3) 1:1 mixture of the two

Answer 42

In order to “prove” that we have successfully extracted/purified myristic acid

Question 43

Why is it insufficient to solely take the MP of myristic acid as a method of identifying that you have successfully extracted it?

Answer 43

The MP difference between myristic acid and trimyristin is within 5 degrees of each other

Trimyristin = 56 C
Myristic Acid = 54 C

Therefore, the MP you see for myristic acid could also be the MP observed for trimyristin

–> Taking the MP of just myristic acid and comparing it to the literature value would tell you that you have myristic acid or trimyristin but not which one (as it could very well be either)

Question 44

How do we “prove” the successful extraction/purification of the myristic acid?

Answer 44

Through MIXED MELTING POINT ANALYSIS

Question 45

Why does the mixed melting point “prove” that we have successfully extracted/purified myristic acid?

Answer 45

Because if the mixture MP is depressed, this denotes the presence of the myristic acid!

If the mixture were just trimyristin, the MP would not be depressed and therefore would tell us that our collected sample was NOT myristic acid

BUT if the mixture of the trimyristin and our sample has an MP that is depressed, this tells us that trimyristin is not the only component present and therefore myristic acid must be present in our sample

Question 46

How else can we “prove” successful extraction of myristic acid (OTHER than mixing with trimyristin)?

Answer 46

You could mix your sample with PURE MYRISTIC ACID

–> If the mixture produces MP that is NOT depressed, this signifies that your sample has myristic acid!

–> If the mixture produces MP that IS depressed, this would signify that your sample is NOT myristic acid