5b Flashcards
whats an imine
R R = NR
whats the pH of an imine
4-6
how do we form an imine
ketone + primary amine
acid catalyst: H+
describe imine formation from a ketone and a primary amine
O on C=O attacks H+
loe pair on amine attacks C
1-2 addition
base deprotonates the amine
OH is protonated
lone pair on amine helps remove water LG.
giving us an imine
what is an imminium ion
R R = N R R +
whats an organometallic
C - METAL
in organometallics,, what are the charges
C is slightly -
Metal is slightly +
organolithium
C-Li
organomagnesium
C-Mg X
in organo magnesium,, what can X be
Cl
Br
I
what do organometallics do
undergo nucleophilic addition reactions with ketones + aldehydes to give alcohols
what are organometallic reactions usually carried out in
THF
Et2O
aprotic solvents
bromobutane + Li in Et2O
alkyl lithium
the charges on the C and substituent switch!!
from C being +
to C being -
gives LiBr as a product aswell
bromobutane + Mg in Et2O
alkyl magnesium bromide
Grignard reagent
charges switch from C+ to C-
adding alkyl lithium to ketone // aldehyde
R-Li bond donates e- and attacks the C=O
= e- move to the O giving O-
O- then attacks H3O+ to give an alcohol.
either secondary or tertiary
reaction that forms alcohols from ketones or adehydes
1,2 addition
irreversible
making primary alcohols with MgXOH
H C=O H formaldehyde
the bond between MgX - R attack the C
then reacting with H3O gives an alcohol,, primary
what do we react carbonyls with to get alcohols
alkyl lithium
MgX - R
whats special condition needs to be present when making alcohols using R - MgX
in needs to be in anhydrous conditions as its sensitive to water
how do we synthesise a carboxylic acid
react R - MgX or R -Li with CO2
CO2 addition reactions
Co2 must be solid and in THF or Et2O
reaction for making carboxylic acids from CO2 and R-MgX
R-MgX bond attacks the C in CO2
attacks H3O+ to protonate the O- and give an alochol // carboxylic acid group
bromo butane to carboxylic acid!!
bromobutane + Mg in Et2O
gives butane - MgBr
add solid CO2 electrophile
gives butane CO2MgBr
add H3O+
gives butane - CO2H
addition of a metal hydrides to ketones or aldehydes
gives alcohols
metal hydrides
NaBH4
LiAlH4
what type of H do metal hydrides have
nucleophilic
the B-H or the Al-H bond attack smt positively charged
ketone + metal hydride
secondary alcohol
aldehyde + metal hydride
primary alcohol
bromonium ion
BH4 -
- charge as B is in group 3
BH3
6e- in the B-H sigma bonds
1 empty p orbital
organolithium derivative
R - Li
organolithium derivative charge
C = p-
Li = p+
steps to think of mechanism for organometallics
- is the product a 1, 2, 3 alcohol
- reactant probably had one less carbon
- e- need to come from a C-Metal bond so add the Metal
if product is a 1 alcohol the reactant must be
H H =O formaldehyde
if the product is a 2 alcohol the reactant must be
aldehyde
if the product is a tertiary alcohol the reactant must be
a ketone
what are organometallics used for
they react with aldehydes and ketones,, aka carbonyls,, under 1,2 irreversible reactions to form alcohols.
what must be used when an organometallic reacts with a carbonyl under 1,2 addition irreversible reactions
THF
Et2O
aprotic solvents
what conditions must organometallic,, 1,2addition irreversible reactions be done in
anhydrous
organometallics are strong bases ,, aka they readily react with water/alcohols
product of using organometallics
MgXOH
LiOH
organometallics + CO2 electrophile gives
carboxylic acids
carboxylate salts
halogenoalkane to carboxylic acid reaction
halogenoalkane + Mg + Et2O gives an organomagnesium derivative
add CO2 and H3O+
forms a carboxylic acid
an addition reaction can also be a what reaction
reduction reaction
why must NaBH4 be used instead of NaH
NaH is a strong base bc the H- have a large charge density
this is bc H is more electronegative than sodium
where must the arrow start when drawing an addition // reduction reaction using BH4 or AlH4
from the X-H sigma bond
what solvent must be used in reduction reactions // addition of metal hydrides
THF
reduction reactions can also be called
addition reactions of metal hydrides
borohydride anion
BH4 -
borohydride anion to borohydride
react it with an electrophile to remove 1 of its Hs
leaves u with BH3 : 6e- in the sigma bonds,, 1 empty p orbital
and H-Electrophile is also a product
ester with LiAlH4
primary alcohol
double reduction
ester with DIBAL
aldehyde
what must be done to DIBAL before it ca be a reducing agent
must form a lewis acid-base complex
ester and NaBH4
cant reduce esters
lone pair on O,, pi donation via mesomeric effect which reduces the p+ on C,, making it less reactive
1,2-addition of a hydride is what
a reduction reaction
what does dibal look like
>
- Al - - <
doot doot claw ,, doot doot claw
then a H bonded to the Al
- Al - - <
limitation of LiAlH4
cannot be used in protic solvents
is NaBH4 the more powerful hydride donor aka reducing agent
no
LiAlH4 is the more powerful hydride donor aka reducing agent
esters can be reduced to what using what
esters to aldehydes using DIBAL
esters to primary alcohols using LiAlH4 in Et2O (double reduction)
mechanism of ester to aldehyde
use dibal
O: attacks the Al
H of dibal attacks C
lone pair on O removes O-R of ester
O-R of ester attacks Al
O is - Al is +
electrons from O-Al bond to Al
aldehyde is formed
what is reductive amination
reducing imines to amines
whats an imine again
R R = N R
whats used to reduce imines to amines in reductive amination
Na(CN)BH3
what is Na(CN)BH3
sodium cyanoborohydride
toned down version of borohydride,,
CN withdraws e-,, makes it a weaker reducing agent
mild hydride donor
imine to amine synthesis
reduction called amination
uses Na(CN)BH3 as a mild reducing agent
done at pH6
selective to imines instead of aldehydes//ketones
primary amine
N bonded to 1c and 2 h
secondary amine
N bonded to 2 c and 1 h
tertiary amine
N bonded to 3 c and o H
still has a lone pair tho.
iminium ion description
imine: R R = N R
iminium ion: R R = N(+) R R
natures most important oxidising agent
NAD+
natures most important reducing agents
NADPH
NADH
