Ho that the cycloaddition of two olefins to form Procedure a cyclobutane cannot
ID: 303717 • Letter: H
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Ho that the cycloaddition of two olefins to form Procedure a cyclobutane cannot proceed via a concerted In an effort to make some more "green," we have replace organic solvent toluene with polyethylene glycol d the classical involve an intermediate. The Diels Alder reaction is an industrially very (PEG 200) important reaction in the synthesis of insecti cides and pharmaceuticals. It is a very efficient Diels-Alder Reaction reaction, as both reagents are completely incor Weigh out an amount of maleic anhydride be- porated in the product tween 180 and 200mg and place it along with a magnetic stirrer in a 10mL round-bottom flask. Equip the round-bottom flask with Required Reading reaction, organic textbooka water condenser and add 1mL PEG 200 (polyethylene glycol MW 200). Calculate how much 2,3-dimethyl-1,3-butadiene (d 0.72g Alm of the Experiment Perform a Diels-Alder cycloaddition. mL) should be added to achieve equimolar conditions. Add 2,3-dimethylbutadiene to the flask and heat the reaction mixture slowly to Hydrolyse the intermediate product. * 60-70 °C for about 30 minutes. Learning Objectives Run two consecutive reactions Workup Pour the reaction mixture into a beaker containing-50 mL water to precipitate the cycloaddition product. Determine the melting point (lit. m.p.78-79 *C) and yield. Record the Learn how to work with a low boiling liquid. · Experience the use of greener solvents. IR spectrum of the anhydride. .Learn different workup procedures based Hydrolysis To hydrolyze the cyclic anhydride to the diacid mix the crystals with approximately 10 mL of 25 % acetone/water in asmall (50 mL) beaker. Add 2-3 drops of concentrated HCl as catalyst and a magnetic stir bar. Heat to 60-80 °C for 15 minutes; do not allow the reaction mixture on solubility Comment on Lab Procedures for Second Semester Organic Chemistry Lab As a student you might find the style in which the lab procedures for second semester areto boil. Stir well continuously written somewhat disconcerting and terse These procedures are written in the style used in publications in the literature. They doAfter 15 minutes, remove from heat, and then not have any great detail, but they do pro-cool in an ice bath. Suction filter, rinsing the vide you with all the necessary information Workup to rely on your knowledge of the techniques information is also provided in the Notes. needed to run the experiment. You wilc you learmed in first scmester lab. Addinalind record the IR spectrum using the IR crystals with a minimal amount of cold water Determine the melting point (lit.' 204 C) and 98Explanation / Answer
General information:
Diel’s Alder reaction is one step, concerted reaction there is not formed intermediate and highly stereospecific.
Syn-addition takes place between maleic anhydride and di-methyl butadiene.
It is (4 + 2) pi cyclo addition reaction, di-methyl butadiene (4 pi electron acts as diene) and maleic anhydride (2 pi electrons acts as dienophile), cyclized to give cyclohexene having one double bond where stereochemistry retained (Syn-addition).
q. 1
From I-step, cyclic anhydride is formed from D. A. reaction
In IR spectrum of anhydride, lone pair of oxygen is conjugated to carbonyl group and
Asymmetric and Symmetric C=O coupled stretching vibrations are observed at ~ 1825 and ~ 1758 cm-1(Fermi resonance).
And C-O stretching vib observed in the region 1300-1050 cm-1 (strong) .
After hydrolysis,
Anhydride hydrolysed in the presence of acid and gives dicarboxylic acid.
In carboxylic acid, A broad absorption band observed at 3000-2800 cm-1, due to precence of –OH of carboxylic group and it is observed low shift than simple alcohol due to presence of (intramol. hydrogen bond), hence indicating the formation of acid, which is not observed in anhydride.
Carbonyl absorption band (Sharp) also observed at 1719 cm-1 again indicating the formation of carboxylic acid, which is not observed in anhydride.
And in Both, >3000 cm-1, due to double bond CH absorption band.
2. a. The formation of cyclic anhydride has low M.P. 78-79 oC, If observed M. P. near about up to 74-75 then product will be formed but very less impurity more.
b. Anhydride has low M. P., weak forces of intermolecular present but dicarboxylic acid will be formed, after hydrolysis, and there is intramolecular hydrogen bond present, Polar molecule, strong intermolecular forces present, increase the M. P.
3. Since Diel,s Alder reaction is completed via 1:1 mol of both reactant.
If we taken 0.4 g of maleic anhudride (98 g= 1mol) then required di methyl butadiene(82 g = 1mol) will be:
= 82X0.4/98 = .3346 g
Density = mass/volume
V = M X d
V = .3346 X .72
.2409 ml
Since di methyl butadiene(82 g = 1mol) and maleic anhudride (98 g= 1mol), therefore extra amount of di methyl butadiene is needed.
4. Since medium has PEG which is water soluble and Carboxylic acid is polar and soluble in water as well as in PEG, and anhydride is soluble in ether.
Therefore we can separated by di ethyl ether through separating funnel, Etheral soluble will be anhydride and insoluble layer will be carboxylic acid.
Minimum amount of ether will be taking three times aproximately.
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