Acknowledgment We would like to acknowledge the participation of the students of CHM 266 a t Purdue University Calumet for their assistance in developing this experiment. Literature Cited 1. Tsehitsehibabin, A. E.:Kuindshi, B. M.; Benewolensksja, S. W. Chem. Ber 1925.58, ,6R"
2. (a)Bluhm,A. L.; Weinstein,J.;Sousa,J.A. J. O q . Chem. 1965.28,1989. lbl Soups. J. A,:Weinstein, J. J. Org Chom. 1962.27, 3155. 3. Nunn,A. J.;Sehdeld, K J Chom. Soc 1952, 583. 4. (a)Ault,A.: Kouba, C. J Chem. Edue. 1914,51,39S. (b) Hamood, L.M.: Moody, C. J. Erpatimm~tmOrgcnic Chemistry; Principles and P m c f ~Blackwdl , Scientific Ribliestions: Oxford, 1989. p 696. lc> Eaton. D. C. labomto7 lnv~stigorionrin O~gonicChamLll~; McDraw-Hill: New York. 1989, p413. S. Mayo, D. W.; PIke, R. M.: Buteher, S. S. Micm.eok Organic laboratory; Wiley: New York, 1989, p 303.
Direct Collection of Distillation Fractions into Vials: A Method for the MicrolSemi-Micro Scale Laboratory David Jordan Potsdam College Potsdam NY 13676 The use of standard-taper 14120 glassware for collection of distillation fractions, where the commonly availahle vessels are capable of holding 5-25 mL, presents some disadvantages. Some receivers, such a s round-bottomed flasks, may be too large for small samples or be poorly configured . others (e.e..,madfor concentration of small s a m ~ l e,swhile uated receivers) may be expensive. Often, once a distillate is collected. it must then be transferred. with some loss of material, another container for storage. An inex~ensiveand s i m ~ l svstem e was develo~edfor collection of ;mall samples dLectiy into their storage containers. This svstem, shown in the figure. works well when used with i4120glassware and couldbe used with any glassware having a drip tip that extends beyond the joint. Changing receiver vials requires only unscrewing one vial from the cap, which is held in place by the tubing, and replacing it with a n empty vial. No clamping of the tubing is necessary The open-top cap is held snugly within the tubing during all operations. A vial is firmly held by the cap when only the slightest resistance to clockwise turning
.
rubber Nbing open topcap O-ring
-
0 i
F 2
,
0
U
1. Put the cap and O-ring on the vial. 2. Push me cap into a tubing end.
3. Slide this assembly onto the 14/20 joint, positioning the drip tip
through the hole in the vial cap.
Assembly of a connection between 14120 joints and screw cap vials.
of the vial is encountered. With drip tips of greater than 6-mm dia., i t may be possible, with considerable effort, to s e a t a vial so firmly into t h e cap t h a t t h e O-ring i s squeezed to form a seal around the drip tip. This is to be avoided because it would create a closed system. Such a system also may be used to collect samples by vacuum distillation a t pressures attainable by a water aspirator when small, structurally sound vials are used and, if appropriately modified, may he used to remove small volumes of volatile solvents by connecting a vial to a 14/20 joint of a rotary evaporator.
Parts Used A sample vial that accepts size 13-425screw caps, such as a Wheaton 2-mL Shorty vial or a Wheatan 4mL sample vial. Calibration marks may be easily put on the uniformly cylindrical vials for reliable monitoring of volumes collected. Vials with calibration markings (no longer inexpensive)are available from Wheaton. Heavy-wall gum rubber tubing of a 30-mm length, for example, Fisher Cat. No. 14-175F that is a 12.7-mm I.D. heavywall (6.4 mm) gum rubber tubing. O t h e r sizes of heavy-wall gum rubber tubing or gum stoppers bared to provide a 12.7 mm I.D. tube. 'Wheaton Cat. No. 240508 apen-top cap. A size #7 O-ring. . A Kimax #45005 vacuum adapter and a Chemglass shortpath distillation head are examples of suitable glassware.
Semimicroscale Organic Chemistry Patrick lash; Samuel ~ h i r i ?and Gita ~ukherjee' University of Zambia Lusaka, 10101,Zambia Although microscale e x ~ e r i m e n t shave been widelv -" adopted f& introductory organic chemistry courses in the United States, they are found less often i n developing countries. For example, microscale organic apparently has made negligible inroads in most universities in southern A f r i ~ a There .~ are two major reasons for this: (1) the lack of information and (2)the cost of elassware and e o u i ~ m e n t to convert to microscale, of whi& the second is the more important. We feel that many universities, particularly in developing wuntries, would adopt the microscale approach to organic if it did not involve conversion costs and if pretested experiments could be provided. Experiments done in test tubes with other readily availahle equipment can bring the advantages of increased safety, decreased time, and lower cost to a much broader audience. We hope this note will encourage others to report on test tube-type experiments and other low cost alternatives to traditional scale experiments.
..
'Kent State University-Ashtabula Campus. 3325 West 13th, Ashtabula, OH 44004. '~epartment of Chemistry, University of Zambia, Box 32379, Lusaka. 10101, Zambia. 3None of the four other southern African universities visited by PJF was using microscale.and SP related that he had heard of no rnrcroscale work in other neighboring countries. (Cont~nuedon n u t p a g e )
Volume 71
Number 1 January 1994
A5
the microscale laboratory Experiments Converted to Test Tube Scale Synthesis
mass of percent limiting red'n vs reagent old scale
Microscale version in:
0.400 g
NO
NO
0.186 g
Yes
Yes
0.860 g
No
NO
0.210 g
No
No
0.500 g
Yes
No
0.500 g
NO
NO
, ,
1. nitration of chlorobenzene 2. acetylation of aniline 3. Mn04-cleavage of cyclohexene 4. benzoylation of aniline 5.acetylation of salicylic acid 6. isomerization of maleic to fumaric acid 7. nitration of methyl benzoate 8. nitration of bromobenzene 9. condensation: aceto phenonel benzaldehyde 10. Knoevenagle synthesis of ferulic acid 11. Stereochemistryof addition of Br2
Acknowledgment PJF wishes to thank the J. William Fulbright Foreign Scholarship Board and the United States Information Agency for a Fulbright award to lecture a t the University of Zambia for the 1991-1992 academic year and the University of Zambia chemistry department for graciously hosting this author. Literature Cited 1. Claret, P. A. Small Smle Or@nicPr~pamtions;Pitman: Landan,1961;p 15. Maw,D.W.:Fike,R. M.: Butcher, S. S. Micmsmk Orgonlc Lohmtwy; Wiley: New York, 1986. 3. Williamson. K L. Mlcmsmb OrgonlcErprrimnfs;Heath: h u n g t o n , 1987. 2.
0.560 g
Yes
No
0.560 g
NO
NO
0.466 g
NO
NO
0.500 g
NO
NO
0.200 g
NO
No
The following test tube-scale organic experiments were developed while PJF was a Fulbright teacher a t the University of Zambia during the 1991-1992 academic year.
Results The three-year organic lab sequence a t UNZAconsists of some 50+ labs of which 39 are synthesis oriented and 11of which have been converted to the microscale. These are listed in the table along with expected yields and notes about whether the syntheses appear i n two popular microscale lab texts. (Yields are for recrystallized products except for experiments 9-11 where yields are for crude product.) All experiments used common 15 x 150-mm test tubes a s reaction and recrystallization vessels with no standard taper ware required. Weighing was done directly into a test tube held upright on the three-place balance using a 3x 3 x 5 cm piece of scrap polystyrene block with a hole to accept the test tube. The block makes it possible to keep the total mass of test tube and support low enough so that the balance does not switch to the two-place mode. Refluxing was accomplished via a n air condenser consisting of a glass tube inserted through a rubber stopper while heating was achieved with water or sand baths on a hot plate. Drying tubes were glass tubes crimped near one end, plugged with glass wool and filled with a drying agent. They were attached to the reflux tube via a short length of vacuum hose. Vacuum filtration was accomplished with a regular gravity funnel fitted with a "nail" (1) and a small piece of filter paper. The nail was made by cutting a short length of glass rod and flattening the end. When slipped into the top of the stem of the funnel, the flat A6
surface of the nail provides a surface to support the filter paper. All these reactions produce solid products, because we have not been able to figure out how to do small-scale distillation without purchasing special equipment. Suggestions on how to do small-scale distillations using inexpensive or easily fabricated equipment would be appreciated. Copies of the experiments can be obtained from the author.
Journal of Chemical Education
Small Scale Determination of pKa Values for Organic Acids Patrick Flash Kent State University-Ashtabula Campus 3325 West 13th,Ashtabuia, OH, 44004 A commonly treated structure-activity relationship in beeinnina oraanic chemistrv is the one between acid structure and&ky. This example of a Hammett relationship, a linear free e n e r w relations hi^. is iust one of a vast number of such relationships and ''&;ether they make up what i s perhaps the greatest accomplishment of physical organic chemistry'' (1). General chemistry lab texts occasionally have a n experiment in which the pK, of a n organic acid is determined by titration. At the microscale level, Thompson's text (2)has a semi-quantitative determination for the pK, of acetic acid done by a colorimetric titration. but neither T h o m ~ s has an experiment that is quantilativr. son nor ~ i l i r3t Determination and interwetation of thc DK, values fnr a series of organic acids a s concrete exampie i f the effect of structure on acid strength does not appear to be a n experiment found in the typical organic lab text. This note describes a small-scale lab that takes less than an hour to carry out, and illustrates the effect of structure on acid strength. Two sets of acids were selected for examination, mainly because they were available in the stockroom. The pK,s for formic, acetic, and chloroacetic acids were determined in water. In contrast, the pK,s for benzoic, salicylic, anthranilic, andp-nitro benzoic acids were determined in a n ethano1:water mixture (1/3:213j due to their insolubility in water alone. Calculation of the theoreticalK, or pK, value for a weak acid, HA, is accomplished readily using the equilibrium constant expression for ionization of the acid, HA,
or via the Henderson-Hasslebalch equation
