Alcohol Reactions - HBr, PBr3, SOCl2 - Free Educational videos for Students in K-12

Alcohol Reactions - HBr, PBr3, SOCl2 - By The Organic Chemistry Tutor

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00:0-1	in this video , we're going to go over reactions
00:03	associated with alcohols . So what's going to happen if
00:07	we react and alcohol with hydrochloric acid , the O
00:12	. H group will be replaced with a booming adam
00:15	. So that's going to be the end result .
00:18	And so basically the alcohol is converted into an alcohol
00:22	light . But now let's go over the mechanism for
00:25	this reaction that we have a primary alcohol . And
00:29	so the mechanism will go through an S . And
00:32	T . Reaction . But the first step in this
00:35	reaction will be pronation of the O . H group
00:39	. The O . H group is a bad leaving
00:41	group , but once you add a hydrogen to it
00:44	, it becomes a good leaving group . So the
00:48	oxygen is going to acquire a hydrogen turning into this
00:52	species . And so whenever the oxygen has a positive
00:57	charge , it becomes about to leave the group .
01:01	In the 2nd step , the bromide ion , which
01:05	is now in the solution will attack from the back
01:08	in an S and T . Reaction , expelling H
01:10	21 and so that's how we can get our alcohol
01:14	headlight . So that's the mechanism for the conversion of
01:17	a primary alcohol into an alcohol . Light . Primary
01:23	alcohols react very slowly with hydrochloric acid due to the
01:28	fact that chloride is a weaker nuclear file than bromine
01:33	. However , this reaction can be enhanced if we
01:37	use sync chloride , which is a powerful lewis acid
01:41	. And so this is known as the Lucas regent
01:45	. So this oxygen is going to attack zinc chloride
01:51	but I need to draw this better . So I'm
02:00	going to draw a zinc chloride like this so the
02:04	oxygen attacks sink and it's going to expel a chloride
02:08	ion . And so we're going to have an oxygen
02:12	that's attached to a hydrogen and the zinc species .
02:19	So right now the oxygen has a positive charge ,
02:22	which means it's a good leaving group . So in
02:25	the second step , the chloride ion comes in ,
02:28	it attacks the carbon kicks out the oxygen and so
02:32	that's how we can get our , I'll kill hey
02:35	life . So if you want to convert an alcohol
02:39	into an alcohol chloride where you have a primary alcohol
02:44	, you want to use the Lucas re agent to
02:46	do . So now let's work on some more examples
02:49	. Let's say we have a tertiary alcohol . And
02:52	this time let's react with hydrochloric acid . What is
02:57	the major product in its reaction ? The end result
03:01	is that we're going to replace the O . H
03:03	. Group with the iodine atom . And so that's
03:07	going to be the enemy . So , but let's
03:09	propose a mechanism . So because we have a tertiary
03:13	alcohol , this reaction Will proceed by the SM one
03:19	mechanism . But the first step is pronation . We
03:27	need to convert the hydroxy group into a good leaving
03:31	group . So now because it's an S . M
03:37	. one reaction , the iodide ion , it's not
03:40	going to come in and attack this card and that's
03:42	gonna be an S . And T . Reaction .
03:45	Those method groups will prevent access to this carbon .
03:50	So what's going to happen is that is the lever
03:53	group is going to leave given us a treasury car
03:58	bulkhead in intermediate . And then at this point that's
04:02	when the iodide ion can come in and combined with
04:06	the carbon iodine given us and alcohol , light .
04:11	And so this is the product of the reaction .
04:15	Now let's go ahead and work on another example .
04:21	So let's react this alcohol . This is uh two
04:26	methods cyclo hexane all let's react it with hydrochloric acid
04:32	. So go ahead and predict the major product of
04:33	the reaction and how soon sure mechanism as well .
04:39	So the first step is pro nation , as always
04:42	anytime you react and alcohol with an asset . So
04:53	now we have a good leaving group . So what's
05:00	going to happen is the leaving group is going to
05:02	leave and once it leaves we're going to have a
05:08	secondary carbon cat eye . But notice that the secondary
05:13	car market is next to a tertiary carbon . And
05:16	so when you see that hydride shift will occur .
05:20	And so this is going to give us a more
05:23	stable tertiary carbo Ketan intermediate . And then at this
05:28	point the bromide ion will attack the carbo Can I
05:32	? And so this is going to be the final
05:35	answer . So we have a tertiary alcohol life and
05:40	that's it . Now there are other ways in which
05:44	we can convert alcohols into alcohol . Lights one re
05:49	agent that we could use is PBR three And this
05:53	works through an S . and two mechanism converting the
05:56	O . H . Group into or replace them for
06:00	Berman adam . And so this produces an alcohol bromide
06:04	. Another example Is using s . o . c
06:07	. l . two which also works through an S
06:10	. And T . Mechanism . But this time the
06:12	O . H . Group is replaced with the CIA
06:15	. Now let's go over the mechanism for those two
06:18	reactions . Let's begin by drawn one . Beautiful And
06:26	then PBR three looks like this . This is phosphorus
06:30	try bromide . The phosphorus atom has a lone pair
06:39	. Now phosphorus is partially positive . Yeah the reason
06:46	for that is bro ming is more electro negative than
06:50	phosphorus . So brahman is partially negative . Yeah .
06:57	Now the oxygen in the alcohol also has a partial
07:00	negative charge . So therefore it's attracted to the partially
07:04	positive phosphorus atom . So oxygen is going to behave
07:09	as a nuclear file attacking the phosphorus atom , causing
07:13	one of the bromine atoms to be expelled . And
07:16	so we're going to get an intermediate that looks like
07:18	this . Mhm . Now , whenever oxygen has three
07:29	bonds , it's going to have one lone pair and
07:32	a positive charge . Now , if you recall predominated
07:39	alcohols are highly acidic Whenever you have an oxygen with
07:45	three bonds and the hydrogen on it , that hydrogen
07:51	is going to be highly acidic . So what's going
07:53	to happen next is an acid base reaction . So
08:00	we're going to use the solvent paradyne to remove a
08:04	hydrogen paradigm is a weak base . So paradigm is
08:16	going to abstract a proton , putting these two electrons
08:20	back on the oxygen . So this is what we
08:25	have right now . Now , in the final step
08:35	, a bromide ion is going to attack this carbon
08:40	expel in this group . And so we're going to
08:44	get one bruma butane as our product . And then
08:49	this will be a side product which we can leave
08:52	it like this . So that's the mechanism for the
08:55	reaction of an alcohol with PBR three . This last
08:59	step here is an S . And two step where
09:04	we get inversion at the carbon atom . Now let's
09:08	go over the mechanism of the other reaction . So
09:13	let's start with our primary alcohol . I and let's
09:16	react with vinyl chloride , which looks like this .
09:21	It has a sulfur atom and oxygen to chlorine atoms
09:25	. And the lone pair . Now the oxygen and
09:29	chlorine atoms are more electro negative than sulfur . So
09:33	the sulfur atom has a partial positive charge , just
09:36	like the phosphorus atom . Now the oxygen is going
09:39	to attack the sulfur , causing this pi bond and
09:42	break . And so we're going to get this intermediate
09:57	. So now the oxygen has a positive charge .
10:00	And in the next step the oxygen is going to
10:05	use one of its lone pairs to reform the pie
10:08	bon , expelling a chlorine atom . Yeah . Mhm
10:21	. So this is what we now have . What
10:26	do you think is going to happen next ? Not
10:29	typically this reaction is carried out in purity , and
10:34	paradyne is a weak base which looks like this .
10:43	And the purpose of paradigm in this example is to
10:47	get rid of the hydrogen . In the last step
11:07	, the chloride ion attacks from the back and then
11:11	breaking the carbon oxygen bonds . Those electrons will be
11:14	used to form a pi bond between a sulfur and
11:17	the oxygen atom , and this will expel the chloride
11:20	ion . And so we're going to get this product
11:25	. So this will give us our alcohol chloride .
11:28	We're also going to get sulfur dioxide which looks like
11:31	this . The sulfur has a long period on it
11:35	. So it causes the molecules have a bet shape
11:39	and we have this other chlorate ion . And also
11:41	paradigm has a hydrogen on it . And so that's
11:45	how you can show the mechanism for the conversion of
11:48	an alcohol into an alkali chloride used in S .
11:52	O . C . L . Two in period .
11:53	I mean now we need to discuss the stereo chemistry
11:59	of these reactions . So let's say we have this
12:04	particular alcohol to be , you know , and let's
12:07	react it with hydroponic acid . What's going to happen
12:11	? So you need to know that this will occur
12:14	by means of an S . M . On mechanism
12:15	. Since we have a secondary alcohol . If we
12:18	had a primary alcohol then it would be an essential
12:21	reaction . But secondary and tertiary alcohols react with HBR
12:27	By means of an s . and one mechanism .
12:30	And so we're gonna get every cynic mixture of products
12:33	. So the bromine atom , it could be on
12:35	the dash or it can be on the wedge ,
12:44	but the key is we can get both stereo I
12:46	summers in this example . Now let's say if we
12:50	started with the same alcohol , but this time ,
12:54	instead of using H . B . I , We
12:56	chose to use PBR three . What's going to happen
12:59	now ? This reaction proceeds by an S and two
13:03	mechanism . And so we're going to have an inversion
13:07	at the configuration or at this uh carol center .
13:12	So we're gonna have inversion of configuration and the broiling
13:16	adam is going to be on the wedge as opposed
13:18	to on the dash . So we only get one
13:21	of the two stereo is immersed in this case .
13:26	Mhm . Now if we use S . O .
13:29	C . L . Two , something similar is going
13:31	to happen . So if we use style no chloride
13:43	, It's going to go through an sn two reaction
13:47	. And so we're going to have an inversion at
13:50	the Cairo center but we're going to get a chlorine
13:55	atom instead of a broom in adam . So you
13:58	need to be familiar with the steroid chemistry of these
14:01	reactions . Another one you need to know is TSC
14:06	our in case you see it on the test .
14:10	Mhm . Now this one it works through retention but
14:15	it converts the O . H into a good leaving
14:17	group . And the product that you get is O
14:21	. T . S . Which I'm going to talk
14:22	about soon . So here we have an alcohol .
14:28	And let's put the O . H . Group in
14:30	the front attached to some our group . And then
14:35	we have this compound which is pere it's Halloween .
14:44	It's a final chloride , abbreviated T . S .
14:48	C . O . And so to draw the product
14:52	of this reaction , all you need to do is
14:55	removed hydrochloric acid and simply connect these two groups together
15:09	. And as you can see , you're going to
15:10	get retention at the oxygen . So the stereo chemistry
15:15	doesn't change mm . Now , for those of you
15:23	who need the mechanism , here's how you can show
15:26	it by the way . So this is T .
15:30	S c . O . At the top , and
15:32	this compound is known as our O . T .
15:37	S . So we have an O T . S
15:39	group attach to the our group .

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