Ramon M. Barnes University of Massachusetts Amherst, Massachusetts 01002
Quantitative Laboratory Experiments Based on Reactions of Cythmates
The importance of creating experiments for quantitative and instrumental analysis laboratories which demonstrate both fundamental chemical measuring principles and practical industrial or commercial analysis cannot be too strongly emphasized in today's chemistry curriculum (1). Consistent with this philosophy, this report outlines a series of cohesive experiments based upon reactions of cyclamates for use in an introductory instrumental analysis laboratory. Cyclamates were of particular value because of recent wide public interest and puhlicity (2) and what appeared to be a lackof characterization of cyclamate reactions and determinations. The approach taken in the design of these experiments was to employ directly or with modification previously published cyclamate analyses, and to devise open-ended "developmental" experiments based upon analyses which "should work" for cyclamates because of analogy to known methods. The goals of this series of experiments were to develop a more-than routine student interest in the chemical reactions of the analysis, to apply a variety of instrumental measuring techniques, and to lay the ground-work for further research studies. The same approach and goals can be equally well applied to a variety of industrial or commercial products, and this report may serve as an outline for others interested in devising consistent, sequential experiments. Experimental Methods Selection
ments. The first approach is based upon the direct measurement of cyclamate without prior chemical conversion but with some separation steps (6, 9, 11). The second approach is based upon the analysis of cyclohexylamine, which is the acid hydrolysis and major human digestion product of cyclamates (12-15). In the third approach, the reaction between cyclamates and nitrous acid can be monitored and reaction products measured (6, 16, 18, 19). Because of limited laboratory time, a determination should be completed during a single 4-hr laboratory session. As a consequence, analyses based upon the lengthy hydrolysis of cyclamate were not included in these experiments. Once cyclohexylamine has been formed, however, the analysis times are within that allocated. Table I.
(a)
I (c)
Experimental Methods Used for the Determinotion of Cyclamates
spectrophotomet~ic Determination of CyolamatcFerroin Complex sfter Separation of Saccharin ( 8 ) Soeotro~hotometric Determination of Saccharin-Ferroin Cimplei (16) (Optionhi) Infrared Determination of Cyclamate and Saccharin (10, 17) (Optional)
11. Titrotion with Nilroua Acid (0) Electrochemical Endpoint Detection of CyolamateNitraus Acid Titration (4) (6) Speotrophotometrio Titration of Cyclamate with Nitrous Acid iDeudopmental) 111. Rcoelion Role Melhod with Nitrous Acid (a) Cyclamate Determination Baaed Upon Rate of Reaction with Nitrous A d d (Developmental)
The analytical chemistry of cyclamates prior to 1967 .was reviewed extensiv ly by Richardson (3) who has also developed two rapid cyclamate determinations (4, 5). A number of new determinations have been developed since Richardson's review (6-9). Cyclamates are sodium and calcium salts of N-alkyl-substituted sulfamates in which the alkyl substitution is cyclohexane (10). The chemical analyses are based upon relatively few d i e r e n t chemical reactions. In addition to classical elemental, gravimetric, volumetric, and separation techniques, cyclamates or cyclamate reaction products have been determined by spectrophotometric, electrochemical, and chromatographic methods. This variety of alternate approaches is ideal for the generation of a coherent series of laboratory experiments. The selection of experimental methods for our instrumental analysis course was based upon four criteria: (a) the students' level of chemical sophistication and background, (b) the students' laboratory time limitations, (c) the techniques designated for the course, and (d) the instrumental apparatus available. Three approaches to cyclamate analyses were considered in developing the subsequent laboratory experi272 / Journal of Chemical Education
IV. Nilraus Acid Rsootion Products
Chrom&to~rwhy of Orghnio Reaction Produots (6.18) Determination of Cyelohexene by CoulometrioaUy-Generated Bromination Quantitstive Infrared Determination of Organic Reaction Produots (16) Polsrographia and Speotrosoopio Determination of Lead after Reaction with Sulfate (181
(4 Gas Liquid (b) (c)
(d)
V. Tilrotion of Acid F o m a of Cyclamate ond Saccharin (01 Potentiometrio. Conduotometric, and Thermometric Titrations (Develoomental) (81
A series of experiments, listed in Table 1,was devised, tested, and employed during three semesters of instrumental analysis by senior undergraduates and firstyear graduate students. Additional chemical investigations were encouraged by optional and developmental experimental sections. As additional results were obtained, new experiments were written and integrated into the series. Outline of Experimental Procedures
Although many of the experimental methods are taken from the literature, a number of modifications were necessary for our applications. I n addition, student operating procedures were often tutorial. Conse-
Toble 2. Cyclamate and Saccharin Cantenl of Some Commercial ProductsCalcium Cyclamate
Product
.,",
,%)
Pillsbury Sweet-10 (liquid) Abbott Suoaryl (liquid) Abbott Sweetness and Light (powder) Albert-Cuiver Sugsr Twin (powder) Pillsburv Funny Faoe (powder) General Foods Scoop (povder) Cooa-Cola Freaoa (liquid) Pepsi-Cola Diet Fountain Syrup (liquid) Country Club Slim-Line Orange (liquid)
8.4 8 6
Calaiurn Saooharin 1%)
0.7
0.8 0.45 1.8 1.9 1.4b 0.01
7.2
25.2 3.4 0.2
