Question

Keywords: phosphorus-chlorine bond; organophosphin Techniques: various techniques are summarized in the Technique Tips section of the ure to read through the relevant ones before starting t be found in the appendices on the course website web site. Be the experiment. Useful information can also Phosphorus has the common oxidation states of III and V and it is known to form an extensive rang of organic compounds in both oxidation states. Phosphines of the type PR,R,R, have the s. If R is phosphorus(III). Oxidation to phosphorus(V) can be quite casy, depending on the R group an alkyl, then these phosphi phosphines are fairly stable solids. If R is an alkoxy group, the stability is somewhere In this particular experiment, a phosphine of the type R,-OH, R' = R3 = OEt or 'OPr i prepared ines are quite air-sensitive, smelly liquids. If R aryl, then the in between s to be ction of PCl, with the corresponding alcohol. In principle, this phosphorus(hil) compound could rearrange to O-PH(OR), so that the phosphorus assumes an oxidation state of five It should be possible to determine by spectroscopy which form it prefers Your instructor will tell you whether to use ethanol / first-termers) or iso-propanol (second-termers) in your synthesis. Procedure: The hexanes used in this reaction must be dried over molecular sieves for at least 24h. There is a specially marked bottle in the solvent cabinet. Set up a 100 mL. 2-necked round bottomed flask with a dropping funnel for reflux under nitrogen Get your TA to check the set up of equipment before adding the reagents. Add phosphorus trichloride (4.0 mL, 6.3 g) and dried hexanes (10 mL) to the flask. Add 100 % ethanol (9.0 mL) or so-propanol (12 mL) and dried hexanes (10 mL) to the dropping funnel Bring the contents of the flask to reflux and then begin the dropwise addition at a rate that will take about I h for complete addition. As this is an exothermic reaction, monitor the solvent/vapour boundary in the condenser to ensure that it does not rise too high (the variac setting should probably be below 40% at this point). After the addition is complete, reflux for a further 0.5 h Once the reaction has cooled, reconfigure the apparatus for a vacuum distillation through a multi head receiving adapter. The vacuum will be created by the mechanical pump through the vacuum line, so you will need to be checked out on this with the instructor. Set up the glassware and have it checked before beginning either to pump or to heat.

why do I use dried hexane? what does it do?

Answer 1

Solution:-

We are using phosphorus trichloride in this reaction , phosphorus is in plus three oxidation state with P-Cl bond and we know that P-Cl bond can be easily hydrolyzed to eliminate HCl in presence of trace of water due to presenc of vacent d orbital on phosphorus and highly polar P-Cl bond hence dried hexane has be to used for the reaction.

0) - H Cl Cl 0ヶ s Po Acue) 1