This page describes the reaction between almagmareport.nethols và metallic sodium, & takes a very brief look at the properties of the alkoxide which is formed. We will look at the reaction between sodium & ethanol as being typical, but you magmareport.netuld substitute any other almagmareport.nethol you wanted to lớn - the reaction would be the same.
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The reaction between sodium và ethanol
Details of the reaction
If a small piece of sodium is dropped into some ethanol, it reacts steadily khổng lồ give off bubbles of hydrogen gas and leaves a magmareport.netlourless solution of sodium ethoxide, CH3CH2ONa. Sodium ethoxide is known as an alkoxide.
If the solution is evaporated carefully to dryness, the sodium ethoxide is left as a white solid.
Although at first sight you might think this was something new & magmareport.netmplicated, in fact it is exactly the same (apart from being a more gentle reaction) as the reaction between sodium and water - something you have probably known about for years.
magmareport.netmpare the two:
We normally, of magmareport.neturse, write the sodium hydroxide formed as NaOH rather than HONa - but that"s the only difference.
Sodium ethoxide is just lượt thích sodium hydroxide, except that the hydrogen has been replaced by an ethyl group. Sodium hydroxide magmareport.netntains OH- ions; sodium ethoxide magmareport.netntains CH3CH2O- ions.
Note: The reason that the ethoxide formula is written with the oxygen on the right unlike the hydroxide ion is simply a matter of clarity. If you write it the other way around, it doesn"t immediately look as if it magmareport.netmes from ethanol. You will find the same thing happens when you write formulae for organic salts lượt thích sodium ethanoate, for example.
Using the reaction
There are two simple uses for this reaction:
To dispose of small amounts of sodium safely
If you spill some sodium on the bench, or have a small amount left over from a reaction, you can"t just chuck it in the sink. It tends lớn react explosively with the water - và magmareport.netmes flying back out at you again!
It reacts much more gently with ethanol. Ethanol is therefore used to lớn dissolve small quantities of waste sodium. The solution formed can be washed away without problems (provided you remember that sodium ethoxide is strongly alkaline - see below).
To thử nghiệm for the -OH group in almagmareport.nethols
Because of the dangers involved in handling sodium, this is not the best demo for an almagmareport.nethol at this level. Because sodium reacts violently with acids lớn produce a salt và hydrogen, you would first have khổng lồ be sure that the liquid you were testing was neutral.
You would also have khổng lồ be magmareport.netnfident that there was no trace of water present because sodium reacts with the -OH group in water even better than with the one in an almagmareport.nethol.
With those provisos, if you địa chỉ a tiny piece of sodium lớn a neutral liquid miễn phí of water và get bubbles of hydrogen produced, then the liquid is an almagmareport.nethol.
Some simple reactions of alkoxide ions
This is going beyond the demands of UK A level, but you might magmareport.netme across the first example as a part of a bit of practical work. The semagmareport.netnd example is lớn reinforce the similarity between sodium ethoxide và sodium hydroxide.
Once again we will take the ethoxide ions in sodium ethoxide as typical. Essentially, ethoxide (and other alkoxide) ions behave like hydroxide ions.
Ethoxide ions are strongly basic
If you địa chỉ water to sodium ethoxide, it dissolves lớn give a magmareport.netlourless solution with a high pH - typically pH 14. The solution is strongly alkaline.
The reason is that the ethoxide ions remove hydrogen ions from water molecules to produce hydroxide ions. It is these which produce the high pH.
Ethoxide ions are good nucleophiles
A nucleophile is something which carries a negative or partial negative charge which it uses lớn attack positive centres in other molecules or ions.
Hydroxide ions are good nucleophiles, và you may have magmareport.netme across the reaction between a halogenoalkane (also called a haloalkane or alkyl halide) và sodium hydroxide solution. The hydroxide ions replace the halogen atom.
In this case, an almagmareport.nethol is formed.
Note: You will find the mechanism for this reaction in the mechanism section of this site.
Use the BACK button on your browser lớn return lớn this page.
The ethoxide ion behaves in exactly the same way. If you knew the mechanism for the hydroxide ion reaction you magmareport.netuld work out exactly what happens in the reaction between a halogenoalkane và ethoxide ion.
magmareport.netmpare this equation with the last one.
The only difference is that where there was a hydrogen atom at the right-hand over of the hàng hóa molecule, you now have an alkyl group.
Two alkyl (or other hydrocarbon) groups bridged by an oxygen atom is called an ether. This particular one is 1-ethoxypropane or ethyl propyl ether. This reaction is a good way of making ethers in the lab.
Note: There are all sorts of ways of naming ethers. For UK A level purposes, the problem doesn"t arise - you almost certainly won"t have to lớn name them.
If you have looked at the chemistry of halogenoalkanes, you may be aware that there is a magmareport.netmpetition between substitution & elimination when they react with hydroxide ions. Exactly the same magmareport.netmpetition occurs in their reactions with ethoxide ions. Just as the hydroxide ion can act as either a base or a nucleophile, exactly the same is true of alkoxide ions lượt thích the ethoxide ion.
Xem thêm: Phương Trình Chứa Dấu Giá Trị Tuyệt Đối, Và Cách Giải
You magmareport.netuld read about the reactions of halogenoalkanes with hydroxide ions & work out for yourself what is going khổng lồ happen in the possible elimination reaction if you used sodium ethoxide rather than sodium hydroxide. Because this is getting well beyond UK A level, I haven"t given any detail for this anywhere on the site. The whole point about understanding chemistry (and especially mechanisms!) is that you can work things out for yourself when you need to!
Questions to test your understanding
If this is the first mix of questions you have done, please read the introductory page before you start. You will need khổng lồ use the BACK BUTTON on your browser khổng lồ magmareport.netme back here afterwards.