|
|
 |
Reply
| | From:  von51895189 (Original Message) | Sent: 2/21/2005 2:03 AM |
Hello~ i'm very stuckkkkkkkkkk......... Does anyone know the reagents and mechanisms for the transformations of: 1.) C6H5=O ----------> C6H5=CH2 2.) C6H5COCl ----------> C6H5COCH3 thank you so much~ :) von |
|
 First
Previous
2-13 of 13
Next
Last
|
|
Reply
| | | From: ·Steve· | Sent: 2/21/2005 3:06 AM |
Hi Von, these are just standard organic reactions as far as the reactions themselves go. In your first reaction, there seems to be a typo or something, because I don't think "C6H5=O" even exists. Possibly it was supposed to be cyclohexanone, or maybe benzaldehyde, C6H5CHO. Anyway, phosphorus ylides react with aldehydes and ketones to give alkenes,
R2C=O + Ph3P=CH2 --> R2C=CH2 + Ph3P=O
(Ph stands for the phenyl group, C6H5-)
+ -
The phosporus ylide has another resonance structure, Ph3P-CH2, (formal + charge on the phosphorus and a formal - charge on the CH2 carbon) where there is a lone electron pair on the carbon with the negative formal charge. The mechanism involves a betaine intermediate which gives the products. For your second reaction, converting an acid chloride to a ketone, you could use a Gilman reagent Li+R2Cu- :
RC(O)Cl + (CH3)2CuLi --> RC(O)CH3 + LiCl + CH3Cu
(The oxygen in parentheses is the carbonyl oxygen, =O.)
The mechanisms may be online somewhere, at least the phosphorus ylide reaction. Mechanism of Gilman reactions are not given in most first year organic textbooks, in the U.S. at least, so that one may be harder to find. You may be able to find one or the other mechanism by doing keyword searches on "phosphorus ylide" and "mechanism" and "Gilman" and "acid chloride" and "mechanism", or something similar.
Steve
|
|
Reply
| |
Hi steve Thank you very much for your help!! you are very helpful~  yes, I think the compound in the first reaction is cyclohexanone, I got it wrong, I can't even name the compound....... -___- May I ask you for more help with another two transformations? I have attached them to this message~ thanx a lot~ von |
| | mechanisms..ppt |
Reply
| | | From: ·Steve· | Sent: 2/22/2005 8:50 AM |
Glad to help, Von. So far I haven't been able to open your attachment. I eventually get an MSN error message if I try to open it, and if I save it first it comes up blank when I open it in PowerPoint (I get the little boxed red "X" instead of the graphic).  I'll try again tomorrow! Steve |
|
Reply
| |
Steve, Sorry to bother you..... I don't know why the file isn't working....  anyway, I have sent it to your email address of [email protected] , is it ok for me to do that? and I have attached it to this message too, hope you will be able to open it~ Many thankssssss von |
| | mechanisms..ppt |
Reply
| | | From: ·Steve· | Sent: 2/22/2005 11:35 PM |
No bother! I got your message at at the chemistrycorner address, but still no luck opening the attachment! The error message says something like, "Unable to open or download file...", even though Hotmail first scanned it for viruses with no error message when I clicked on the attchment. Possibly, the two periods in the filename are causing the glitch. Steve |
|
Reply
| | | From: ·Steve· | Sent: 2/22/2005 11:38 PM |
I forgot to ask, does the attachment open correctly for you when you click on it from your computer? Steve |
|
Reply
| |
I can open the file when I click on it from my computer~ maybe... I can decribe the transformation here to you.... even though I can't really name these compounds.... hope you can understand what I mean : 1.) C6H5COCH3 ------------> C6H5CO2H 2.) Cyclohexanone -------------> A ring with a double bond O and a CHO group attached to it~ sorry about this~ thank youuuuuuuuuu ^ . ^ von |
|
Reply
| | | From: ·Steve· | Sent: 2/23/2005 7:16 AM |
Weeeell, I don't know why I can't open it, but your descriptions are clear enough to tell what the reactions are. The first one is easy, hydrolysis of an ester yields the carboxylic acid + alcohol:
Acid-catalyzed hydrolysis:
RC(O)-OR'  RC(O)-OH + R'OH H3O+
Or, we can use base-catalyzed hydrolysis (saponification) followed by acidification:
RC(O)-OR'  RC(O)-O- + R'OH OH- (aq)
Adding aqueous acid protonates the carboxylate ion to give the neutral carboxylic acid:
H3O+
RC(O)-O-  RC(O)-OH
The second reaction will take some extra steps. Cyclohexanone can be converted to its enolate ion by reaction with a strong base like diisopropylamide, LDA. This will remove an alpha-hydrogen (a hydrogen on a carbon next to the carbonyl carbon) from cyclohexanone to leave the enolate ion of cyclohexanone, with a lone pair and formal -1 charge on one of the ring carbons next to the carbonyl group (where the alpha-hydrogen used to be). These alpha-hydrogens show acidic behavior in this regard, and the enolate ion is really the conjugate base of cyclohexanone. Note also that these enolate ions will have two resonance structures which make their formation easier.
Now, this enolate ion of cyclohexanone can be reacted with alkyl halides if we want to put an alkyl group where the H used to be at the alpha position, or in this case, we can use another carbonyl compound to give an aldol condensation product. If we use formaldehyde, HC(O)H, we will get a CH2OH group next to the carbonyl carbon of cyclohexanone which can be selectively oxidized to the aldehyde group using PCC.
Drawings would be much better, but hopefully this makes sense! Have you studied carbonyl alpha condensation reactions and enolate ions yet? That topic is central to this reaction.
Steve
|
|
Reply
| |
Hi steve~ Thank you for answering my questions  ~ but there's something more I wanna ask you, for the first reaction C6H5COCH3 ------------> C6H5CO2H is C6H5COCH3 an ester? because in the previous post, you said it is a ketone~ are they the same thing? I'm a bit confuse. hope to get your reply von |
|
Reply
| | | From: ·Steve· | Sent: 2/23/2005 11:56 PM |
>> is C6H5COCH3 an ester? because in the previous post, you said it is a ketone << Oooops, my mistake, that is the ketone acetophenone, quite a different compound from the ester, C6H5CO2CH3, methyl benzoate! So, scratch those ester hydrolyses for the time being. Here's a possible procedure:
1) Reduce acetophenone with LiAlH4 or NaBH4 to the alcohol 1-phenylethanol, C6H5CH(OH)CH3.
2) Dehydrate the alcohol using H2SO4 or H3PO4 to form styrene, C6H5CH=CH2.
3) At this point you can oxidatively cleave the double bond by ozonolysis to give benzaldehyde, C6H5C(O)H (plus formalaldehyde, HC(O)H) followed by oxidation of the aldehyde to the carboxylic acid with a reagent such as Jones' reagent. Or, you can oxidatively cleave the alkene group of styrene using hot alkaline KMnO4, which would give the benzoate ion (plus CO2); acidification would then give the desired product benzoic acid.
Steve
|
|
Reply
| |
Hello steve, I wouldn't be able to complete my work without your assistance~ so, thank you for all your help!!! you are very kinddddddddd~ von |
|
|
First
Previous
2-13 of 13
Next
Last
|
|
|
Free Forum Hosting
Important Announcement
Return to Organic