Tch chit cafein t tr, c phTrong th nghim ny, ta s tch mt hp cht hu c c ngun gc t t nhin. lm c nh vy, mt k thut quan trng ta cn tm hiu l k thut lc thng thng .Tri qua 180 nm, trong tt c cc th nghim loi ny th u tin ta cp n ha hc hu c v cc nh khoa hc s dng t "ha hc hu c " c ngha l "ha sinh " ngy nay : l cc cht ha hc ca cc sinh vt sng . Cc nh ha hc hu c u tin quan tm ti s tch chit v xc nh cc hp cht t cc ngun nguyn liu , iu ny cng ging nh ta s lm g trong th nghim ny .

Nh trong tt c cc phng th nghim , ta nn tm cc yu t gy hi nh hng n qu trnh lm vic v vi cc ha cht ta s s dng hoc chun b . Ta cng c th xc nh cu trc ca caffeine v bn lun v l do ti sao phng php ny hot ng da trn nguyn tc .

1. Thy tinh nng ging nh thy tinh lnh. Trc khi nht dng c thy tinh, phi kim tra xem n c nng hay l khng v x l. c bit, quan tm v thn trng v vic s dng dichloromethane khi tip xc vi nc nng.2. Ho cht c mi hoc p sut hi cao khng c s dng bn ngoi, ngoi tr dng trong t ht.3. Nhn ln bn MSDS cho mi thuc th c s dng. Cch tin hnh v quy trnh c th hn c a ra di y.4. NaOH 6M l mt cht n da mnh m. Hy x l n mt cch thch hp..5. Bn nn cn thn trnh b lm sn phm trong vic thc hin cc th nghim. Bn s lm hng kt qu ca bn, cn thn cc mi nguy him lin quan n dichloromethane.6. Bn s c c sn phm t mt hn hp ca 2-propanol (mt dng tinh khit ca "cn") v hn hp hexan, l hydrocarbon. Nhng dung mi to ra c nguy c gy chy, v ht phi mt lng ln c th gy nh hng i vi c th; s dng chng trong t ht.7. Ra tay sau khi hon thnh cc th nghim.

X l:caffeineVt b.dichloromethaneCc dichloromethane bn s dng s c bc hi. Lau bngbng khn giy v cho php cc dichloromethane bay hi trongnp. Khn giy sau c th c hy b trong st rc.Tc nhn lm kh yn trong t ht cho n khi kh; sau cho vo st rc.hexanesDung mi kt tinh phi c t trong cc chai cht thi.2-propanolDung mi kt tinh phi c t trong cc chai cht thi. 2-propanol tinh khit c th c ra xung bn ra.NaOHXi ra bn ra.Ti trVt b trong thng rc.

60

61

B tr v cc dung dch i km

Lm sch bng x phng v nc v x xung bn ra.

Phng phpTrong th nghim ny, bn s bt u s dng kp gi dng c thy tinh ca bn,trong sut qu trnh lm th nghim. Khng ging nh ha hc ni chung, mi th s khng c nhng quy trnh r rng cho bn.S dng theo cch ca bn, tn dng tt c nhng kin thc ca bn, n s gip t cho bn. S dng kp gi nhng th c c; vng dng cho cc dng c hnh cu.

Bn c th cn phi thao tc vi cc dng c thy tinh nng vi kp gp. C mt li ngh rng bn thc hnh bng cch s dng kp gp trc khi bn lm mt ci g

1. Mang 100-120 ml nc un si trong mt cc thy tinh. Trong khi n ang nng, cho vo 6-7 gram c ph hoc tr.

2. Khi nc c un si, thm c ph hoc tr vo nc, khuy, khong 5 pht.

3. Trong khi c ph (tr) c ngm, t b lc c ph (tr) ca bn vo phu lc. Lc c ph (tr) khi n thi gian. Lm mt c ph xung di 35C, s dng mt thau nc .

4. Ngm c ph (tr) 5 ln vi 20-25 ml dichloromethane. Ra cc tp cht hu c kt hp 2 ln vi 20 mL NaOH 6M, v 1 ln vi 20 ml nc. Loi b cc tp cht hu c v kh n (CaCl2).

5. Cho bay hi cc tp cht hu c kh trong mt cc thy tinh,trong t sy.Thu hi cng nhiu sn phm c th t cc thy tinh sau khi dung mi bc hi. Cn sn phm ca bn. C c im nng chy ca cc sn phm ca bn, so snh n vi mt mu ch thc ca caffeine.

Mc d caffeine tinh khit l mu trng, cc d lng bn c c c th l mu xanh l cy hoc mu nu do s hin din ca cht dip lc v tannin. Xc nh khi lng ca sn phm th v tm im nng chy ca n nh th no so vi caffeine.

6. Bo co kt qu ca bn (s lng c ph hoc tr, khi lng ca caffeine thu c) cc ging vin h c th tham kho vi nhng sinh vin khc. So snh kt qu ca bn vi nhng ngi khc lm cng th nghim

1. Nu c thi gian, lc th caffeine bng ti kt tinh.a. t caffeine th ca bn vo bnh erlen 25 ml . un nng mt vi ml 2-propanol cho n khi n gn nh si; sau ha tan caffeine trong dung dch 2-propanol. Gi cho bnh mb. Lm ngui n nhit phng. Khuy cn thn, thm 1 ml hexan v yn trong mt vi pht. Thu thp cc tinh th ca caffeine bng cch lc chn khng trong mt ci phu Hirsch, v ra sch vi mt lng nh hexan.c. Xc nh khi lng v nhit nng chy im ca caffeine tinh khit.

4

3