phenol + hno3

RING REACTIONS OF PHENOL

Bạn đang xem: phenol + hno3

This page looks at the way the reactions of the benzene ring in phenol are modified by the presence of the attached -OH group. It covers the reactions of phenol with bromine water and with nitric acid.

How does the -OH group modify the ring reactions?

Activation of the ring

The -OH group attached to tướng the benzene ring in phenol has the effect of making the ring much more reactive than vãn it would otherwise be.

For example, as you will find below, phenol will react with a solution of bromine in water (bromine water) in the cold and in the absence of any catalyst. It also reacts with dilute nitric acid, whereas benzene itself needs a nitrating mixture of concentrated nitric acid and concentrated sulphuric acid.

If you follow this links, you may have to tướng explore several other pages before you are ready to tướng come back here again. Use the BACK button (or HISTORY tệp tin or GO menu) on your browser to tướng return to tướng this page.

One of the lone pairs on the oxygen atom in the -OH group overlaps with the delocalised ring electron system . . .

. . . giving a structure rather lượt thích this:

The donation of the oxygen's lone pair into the ring system increases the electron mật độ trùng lặp từ khóa around the ring.

A benzene ring undergoes substitution reactions in which the ring electrons are attacked by positive ions or the slightly positive parts of molecules. In other words, it undergoes electrophilic substitution. If you increase the electron mật độ trùng lặp từ khóa around the ring, it becomes even more attractive to tướng incoming electrophiles. That's what happens in phenol.

If you choose to tướng follow this links, use the BACK button (or the HISTORY tệp tin or GO menu) on your browser to tướng return to tướng this page later.

The directing effect of the -OH group

The -OH group has more activating effect on some positions around the ring than vãn others (for reasons which go beyond UK A level). That means that incoming groups will go into some positions much faster than vãn they will into others.

The net effect of this is that the -OH group has a 2,4-directing effect. That means that incoming groups will tend to tướng go into the 2- position (next door to tướng the -OH group) or the 4- position (opposite the -OH group). You will get hardly any of the 3- isomer formed - it is produced too slowly.

Specific examples

Reaction with bromine water

If bromine water is added to tướng a solution of phenol in water, the bromine water is decolourised and a white precipitate is formed which smells of antiseptic.

Xem thêm: (nh4)2so4 ra nh3

The precipitate is 2,4,6-tribromophenol.

Notice the multiple substitution around the ring - into all the activated positions. (The 6- position is, of course, just the same as the 2- position. Both are next door to tướng the -OH group.)

If you choose to tướng follow this links, use the BACK button on your browser to tướng return to tướng this page.

Reactions with nitric acid

The reactions with nitric acid are complicated because nitric acid is an oxidising agent, and phenol is very easily oxidised to tướng give complex tarry products. What follows misses all that complication out, and just concentrates on the ring substitution which happens as well.

With dilute nitric acid

Phenol reacts with dilute nitric acid at room temperature to tướng give a mixture of 2-nitrophenol and 4-nitrophenol.

With concentrated nitric acid

With concentrated nitric acid, more nitro groups substitute around the ring to tướng give 2,4,6-trinitrophenol (old name: picric acid).

Where would you lượt thích to tướng go now?

To the phenol thực đơn . . .

To the thực đơn of other organic compounds . . .

To Main Menu . . .

© Jim Clark 2004 (modified March 2016)

Xem thêm: nano3 + h2so4