Organic- Carbonyls, carb acids, esters Flashcards
what are the reagents and conditions for the oxidation of an primary alcohol?
acidified potassium dichromate and sulfuric acid
heat and distillation
what does the oxidation of an primary alcohol form?
an aldehyde, which can undergo further oxidation via heat and reflux to form a carboxylic acid
what are the reagents and conditions for the oxidation of a secondary alcohol?
acidified potassium dichromate and sulfuric acid
heat and reflux
what does the oxidation of a secondary alcohol form?
a ketone, which cannot undergo further oxidation
why don’t ketones undergo further oxidation?
due to there being no H attached to the carbonyl carbon
do tertiary alcohols undergo oxidation?
no
why does propanal have a lower boiling point than propan-1-ol or propanoic acid?
propanal does not contain an OH bond, so does not involve hydrogen bonding, the strongest IMF. therefore less energy is required to break the bonds, as temporary induced dipole interactions are not as strong
what does tollen’s reagent/ammonical silver nitrate do?
differentiates between aldehydes and ketones/oxidises aldehydes to carboxylic acids
what are the reagents and conditions for the tollen’s test?
ammonical silver nitrate
gently warm in a boiling water bath
how can you tell if an aldehyde or ketone is present during the tollen’s test?
an aldehyde will form a silver mirror/black precipitate of silver
a ketone will not give a silver mirror
what is the half equation that you need to know for the tollen’s test and what does it show?
Ag+ (aq) + e- —-> Ag (s)
it shows the reduction of silver ions to silver
how would you reduce an aldehyde or ketone to an alcohol?
add NaBH4 (sodium borohydride) at room temperature, then dilute sulfuric acid
aldehydes will form primary alcohols, ketones will form secondary alcohols
how many hydrogens do you need in the equation for adding NaBH4 to balance and form the alcohols? *also need to know the nucleophilic addition mechanism
2[H]
how would you convert aldehydes and ketones to 2-hydroxynitriles? *need to know mechanism for this nucleophilic addition
add KCN, then dilute sulfuric acid at room temperature
why do we need to use KCN as well as HCN, which is what is written in the equation?
HCN is a poisonous gas and not a strong enough acid to give enough of the -CN nucleophile, so KCN is used with the conditions
what do aldehydes and unsymmetrical ketones form in the nucleophilic addition of HCN?
a mixture of enantiomers (a racemic mixture)
what are the reagents and conditions needed for the 2,4-DNP test?
2,4-DNP in methanol
room temperature
what is the 2,4-DNP test used for and what would the positive result look like?
to identify the presence of an aldehyde OR ketone
a crystalline orange precipitate
after the 2,4-DNP test, how would you distinguish between an aldehyde or ketone?
by looking at the melting point and matching them up on the data table
do carboxylic acids and esters react with 2,4-DNP?
no
explain how you would identify an aldehyde or ketone? (practical)
1) filter the impure orange solid to separate the solid precipitate from the solution
2) recrystalise the solid to produce a pure sample of crystals
3) measure and record the melting point of the purified 2,4-DNP and compare to the database of melting points to determine the specific carbonyl compound
CH3CH2CH2CHO, CH3CH2COCH3, CH3CH2CH2CH2OH
Describe a sequence of tests to identify which compound is which (6)
1) add each sample to a test tube and add 2,4-DNP to distinguish whether an aldehyde or ketone is present. if present, a crystalline orange precipitate will form. the sample with no precipitate is the alcohol.
2) add fresh samples of those remaining to 2 test tubes, add tollen’s reagent in a boiling water bath which will form a black precipitate of silver if an aldehyde is present. the sample without the precipitate is the ketone.
explain the solubility of carboxylic acids
carboxylic acids tend to be soluble in water due to having a permanent dipole and hydrogen bonding, due to the OH bond present in the functional group. this makes them compatible with water, which also has hydrogen bonding.
what are the products formed from carboxylic acid + metal?
a carboxylate salt + hydrogen
