CARBONYLS AND CARBOXYLIC ACIDS Flashcards
What is tollens reagent used for
what is the process of making it
what is the complex
what do test results show
can distinguish between aldehydes and ketones
add silver nitrate solution to a test tube then add a few drops of NaOH to form a pale brown precipitate
add a few drops of dilute ammonia until precipitate dissolves
then add aldehyde/ketone to tollens reagent and heat in a water bath, (NO BUNSEN BURNER AS ALDEHYDES/KETONES ARE FLAMMABLE)
Tollens complex is [Ag(NH3)2]+
aldehydes - tollens is reduced to silver which coats the inside of test tube
ketones - no silver precipitate formed
How can 2,4 DNP be used for qualitative tests
Bradys reagent is dissolved in concentrated sulfuric acid and methanol and then added to the substance under test
if a ketone or an aldehyde is present, a bright orange precipitate will be formed
ONLY REACTS WITH C=O IN ALDEHYDES AND KETONES
NOT CARBOXYLIC ACIDS
the melting point of the orange precipitate can be tested against a known library of carbonyl melting points
How can aldehydes and ketones be reduced
NaBH4 dissolved in methanol and water
NUCLEOPHILIC ADDITION
sodium borohydride
aldehydes reduced to primary alcohols
ketones reduced to secondary alcohols
Mechanism of carbonyl reduction
H- with lone pair from reducing agent attracted to delta positive carbon from C=O forming a bond
C=O bond breaks and electrons join the oxygen from the bond
H+ from acid or water that was added to the reducing agent at the start will join the O- leaving an alcohol
Carbonyl compound –> hydroxynitrile
Nucleophilic addition with KCN (or HCN)
Potassium cyanide dissolved in acidic solution to produce CN- ions which is a nucleophile
CN- with lone pair attacks delta positive carbon from C=O forming a bond
C=O breaks and 2 electrons transferred to oxygen
H+ from acid solution join O-
Risks of using potassium cyanide and how to prevent harm
irritant and dangerous if ingested or inhaled
can form toxic gas HCN if reacts with moisture
use fume cupboard to prevent toxic fume exposure
wear safety goggles
wear lab coat to prevent contamination
wear gloves while handling
Describe solubility of carboxylic acids
they can dissolve in polar substances like water as they can form hydrogen bonds
they have a delta negative oxygen with lone pairs
and a delta positive hydrogen on the OH group
the hydrocarbon part of the chain is non polar so the larger the hydrocarbon the less soluble to molecule is
Carboxylic acid + carbonate products
salt, water and carbon dioxide
Carboxylic acid + metal
Salt + hydrogen
FIZZING IS SEEN
CAN TEST FOR HYDROGEN GAS WITH SQUEAKY POP
Carboxylic acid + metal oxide
Salt + water
Carboxylic acid + alkali
salt + water
Acyl Chloride functional group
COCl
How are acyl chlorides named
find longest carbon chain then add -oyl chloride to the end
Acyl groups always at the end
How to form an acyl chloride from a carboxylic acid
Add SOCl2 to carboxylic acid which gives acyl chloride + SO2 + HCl
What 4 things can Acyl chlorides react with and what type of reactions occur
Water, ammonia, alcohols and primary amines
ALL REACTIONS ARE VIGOROUS AS ACYL CHLORIDES ARE VERY REACTIVE
Chlorine is always substituted
