carboxylic acid and its derivatives Flashcards
comment on the bp of carboxylic acids
- higher than alc as it forms stronger H bonding than alcohol as O-H bond is more polarised due to presence of electron donating inductive carbonyl group
- carboxylic acid dimerise in the liquid state forming 2 H bonds between each pair of molecules
comment on the solubility of carboxylic acids
lower acids can form H bonds and are soluble but solubility decreases as HC chain increases
why are carboxylic acids more acidic than alcohols
alc - ROH <—> RO- and H+
carboxylic acid - RCO2H <—> RCOO- and H+
in RCO2- ion, the p-orbitals in the CO2- group overlap with one another resulting in RCO2- having a resonance stabilized structure. This helps disperse the negative charge on the O atom, stabilizing it and increasing the strength of acid as POE of eqn 2 lies more to the right than eqn 1
what are the reactions that carboxylic acids undergo
- reaction with reactive metals, acids, carbonates and hydrogen carbonates
- reaction with alcohols to form esters (reversible)
conc H2SO4(aq) and heat - conversion to acyl chlorides
PCl3 and SOCl2 at rtp or PCl5 with heat - reduction to form pri alc
LiAlH4 in dry ether at rtp - decarboxylation to alkanes
soda lime (CaO and NaOH) and heat
how to form carboxylic acids
- From oxidation of primary alc or aldehydes
K2Cr2O7(aq), H2SO4(aq) and HUR for both or KMnO4 … for aldehydes - acid hydrolysis of nitiriles
conc H2SO4 (aq) and heat - side chain oxidation of benzylic H
KMnO4 in H2SO4 and heat
what is a distinguishing test for carboxylic acids
acid hydrolysis to form carboxylic acid as NH3 is produced which turns red litmus blue
which reducing agent is stronger and why - LiAlH4 in dry ether at rtp vs NaBH4 in ethanol
LiAlH4 is the stronger reducing agent due to the larger electronegativity diff between H and the Al as compared to H and B, making the H more electron rich
comment on the bp of acyl chlorides and esters
acyl chlorides and esters dont form intermolecular H bonds as they lack H atom directly bonded to a highly electronegative atom. Thus, molecules are only attracted by weaker pd-pd int so they have lower bp
comment on the solubility of acyl chlorides and esters
esters solubility varies with the R groups while acyl chlorides are very reactive with water
how to form esters
- alc and carboxylic acid with conc H2SO4(aq) and heat
- alc and acyl chlorides at rtp
- phenols and acyl chlorides with addition of NaOH(aq) ( to generate stronger nucleophile C6H5O- )
what reaction does esters undergo
acid hydrolysis or base hydrolysis followed by addition of acid
H2SO4 of NaOH both with heat —> carboxylic acid or carboxylic salt
note: acid hydrolysis is reversible while base hydrolysis is not
how to form acyl chlorides
conversion of carboxylic acid to acyl chlorides
PCl5 with heat or PCl3/SOCl2 at rtp
what reactions do acyl chlorides undergo
- hydrolysis with water to form carboxylic acid
- gives white fumes of HCl - alc or phenol to give esters
rtp for alc and NaOH for phenol - react with ammonia/amines to give amides
compare the ease of hydrolysis of
RCOCl C6H5COCl RCH2Cl and C6H5Cl
comparing the acyl chlorides to RCH2Cl and C6H5Cl, the alpha carbon is bonded to 2 highly electronegative atom, Cl and O, which exerts an electron-withdrawing inductive effect that makes the alpha carbon highly electron deficient and more susceptible to nu attack
comparing the 2 acyl chlorides, C6H5COCl faces more steric hindrance due to the presence of the huge benzene ring making it harder for nucleophiles to approach
comparing the 2 non-acyl chlorides, the p orbitals of Cl in C6H5Cl overlap with the p orbitals of the carbon in the benzene ring resulting in delocalization of lp of electrons which imparts double bond character on the C-Cl bond making it harder to break and less reactive
