[Fragment_Error]

Hey guys I've done this practical at school and just need some clarifying to see if I'm on the right track.

Menthol C₁₀H₂₀O reacts with Sodium dichromate dihydrate Na₂Cr₂0₇ to give Menthone C₁₀H₁₈O

We used 2g of menthol and 20g of sodium dichromate.

1.

Molecular weight:

Menthol: 156.16 g mol ^-1
Sodium dichromate: 261.96 g mol^-1

So to find out how many moles in the quantity used, I go:

2g/156.16 = 0.012

and

20g/261.96 = 0.076


Now to find the theoretical yeild, I use:

0.012 x (261.96/1) = 3.146g

Does that look right?

2.

I've got a question about what "(+) menthone" means. That means that (+) menthone includes all the possible stereoisomers, right?


3.

Ok this question I'm not too sure of. "Why is it important that low temperatures are used during this reaction and that a large excess of oxidizing agent is avoided?"

I'm guessing that low temperatures are used to allow the product to react and prevent solidifying. I'm not sure as to why and excess of oxidizing agent is avoided.

Any hints on that one?


Thanks in advance.

[Dan]

1. No. Think about what the theoretical yield actually means. You have worked out the mass of one equivalent of sodium dichromate. You need to work out the mass of one equivalent of product.

2. The symbol means you have a racemic mixture. It is a 50/50 mixture of enantiomers.

3. It looks to me like you are using a large excess of oxidising agent. Have you seen the MSDS for this compound?

[Fragment_Error]

1. No. Think about what the theoretical yield actually means. You have worked out the mass of one equivalent of sodium dichromate. You need to work out the mass of one equivalent of product.

Ah right, I've only done half of the work for the question!

Still need to do:

0.076 x (156.16/1) = 11.868

11.868g - 3.146g = 8.722g

That should be right.

2. The symbol means you have a racemic mixture. It is a 50/50 mixture of enantiomers.

Ah ok, thanks.

3. It looks to me like you are using a large excess of oxidising agent. Have you seen the MSDS for this compound?

Hmm, then I don't know how to answer this question.

Well actually now I know why it's kept cold, to avoid any sort of combustion.

[Dolphinsiu]

It seems you still don't know what theoretical yield means!

From your rxn given, plz write your reaction first!

                            C10H20O + K2Cr2O7 ------------> C10H18O

M.W.(g/mol)           156.16       261.96                    154.0
No.of mole (mol)     2/156.16     20/261.96                  -
                          = 0.012       = 0.076
                             (Limiting reagent)

For 100% conversion (100% of C10H20O is converted into C10H18O), the yield is called theoretical yield!

Theoretical yield of C10H18O = 0.012 x 154 = ? g

For Q.3,

Plz refer to

http://newsearchch.chemexper.com/cheminfo/servlet/org.dbcreator.MainServlet?action=PowerSearch&query=msds._msdsID%3D15193&sort=&target=msds&from=0&realQuery=entry._structureID%3D2776977&searchTemplate=rn.value%3D%3F+elsor+entry.catalogID%3D%3F+elsor+iupac.value%3D%3F+elsor+mf.value%3D%3F+elsor+%28iupac.value%3D%7E%3F+or+catalog.description%3D%7E%3F%29&searchValue=Menthone&history=off&options=brandqtyoffer&format=plugin

and

http://newsearchch.chemexper.com/cheminfo/servlet/org.dbcreator.MainServlet?action=PowerSearch&query=msds._msdsID%3D11772&sort=&target=msds&from=0&realQuery=structure._structureID%3D3290871&searchTemplate=rn.value%3D%3F+elsor+entry.catalogID%3D%3F+elsor+iupac.value%3D%3F+elsor+mf.value%3D%3F+elsor+%28iupac.value%3D%7E%3F+or+catalog.description%3D%7E%3F%29&searchValue=Menthol&onclick=1&history=off&options=brandqtyoffer&format=plugin

[Fragment_Error]

Cool, thanks for that Dolphinsiu!  As I'm sure you can already tell, I'm not very good at chemistry.

And now for another question: How many stereosiomers does menthone have?

http://i16.photobucket.com/albums/b30/FragmentError/Menthone.jpg

This is what I came up with, 4 stereoisomers.

Am I close?

EDIT: Drew and up loaded pic of stereoisomers.


Actually, one last thing: If citronellol was oxidised under the same conditions (if citronellol was used instead of menthol), what product would you expect to obtain? Why?

Well citronellol has the same molecular formula as menthol: C₁₀H₂₀O but its structure is different. But I'm thinking it would still produce menthone?

[AWK]

I think it has 4 stereoisomers.

OK

[Fragment_Error]

I think it has 4 stereoisomers.

OK

I'm correct in the 4 stereoisomers part? Is the picture I drew correct too?

[AWK]

picture shows only 2 steroisomes.
Draw upper and lower substituents from the same side of ring

[Fragment_Error]

picture shows only 2 steroisomes.
Draw upper and lower substituents from the same side of ring

Like this?

http://i16.photobucket.com/albums/b30/FragmentError/menthone2.jpg

[AWK]

attached

[Fragment_Error]

Ah right, got ya. Thanks heaps. Sorry, it's early morning here, and I should really get to bed.

Just one final question, then I'm going to hit the sack:

Now when doing this experiment, the organic product was colorless, but then a color change occured. Gotta explain the color change.

So I say the menthol goes from C₁₀H₂₀O to C₁₀H₁₈O so the loss of the two H+ ions causes the color change.

[AWK]

After oxidation your product can be impure