Fischer Esterification

Write general reaction

Write out mechanism

What are you looking for in the IR?

presence of small peak in C-H stretch (for methyl group in ester)

absence of OH peak

shift of carbonyl peak

What are potential issues?

1. H+ source from H2SO4 bc we need a strong acid to get reaction started due to carbonyl being bad base

2. Equilibrium Issue (low expected yield, add excess alcohol to fix

3. water present in beginning, use concentrated sulfuric acid to have virutally no water

Yield

Known mutagens?

Sodium Sulfate

Known carcinogens?

Sulfuric acid, sodium sulfate

Severe fire hazards?

Methanol, diethyl ether

Why is water an issue? How do we resolve?

Water is nucelophilic and can be added back as an H+ source and hydrolyze new ester to regenerate carboxylic acid starting material

Run reaction in excess alcohol to drive reaction towards products

Purpose of the sulfuric acid?

Acts as an acid catalyst to protonate the carbonyl oxygen of benzoic acid to make the carbon more electrophilic, so alcohol oxygen can actually react. 

3 things about condenser hoses?

use pins, keep pressure low, in an bottom out on top

nucleophile/electrophile

alcohol oxygen acting as nucleophiile, electrophile is carbonyl carbon of carboxylic acid

Fischer approach

you make carboxylic acid carbonyl carbon a better electrophile by protonating oxygen. now alcohol can attack it, couple more steps we end up with ester

keq?

roughly 4

What is refluxing? Why do it?

The boiling of a solution while continually condensing the vapor by cooling it and returning liquid to reaction flask

To heat solution in a controlled manner at a constant temp

final 6 steps of procedure?

why are NaOH and sodium bicarbonate in an ice-bath before being adding?

because neutralization/ acid-base reactions are highly exothermic

what is biggest safety concern? good practice?

concentrated sulfuric acid, handle carefully change gloves after using

what ° alcohols are needed for Fischer Esterification and why?

1° or 2° bc 3° alcohols are prone to eliminatio

what is the solvent in our rxn?

methanol (the reactant and the solvent so we have 2 uses out of having excess of it)

what are three things we need to deal w/ to prevent product loss? how?

1. proton source- needs to be strong
2. equilibrium- adding excess reactant to drive rxn to the right
3. no products @ the start (H2O)- pure methano

explain using the equation for Keq why adding excess reactant drives the rxn forward

if Keq = 4 which is = to [products]/[reactants], if we add more reactants and 4 is a constant, then to keep 4 constant, the products increases = we make more products!