A CONSIDERATION of the HOW in the TEACHING of ORGANIC CHEMISTRY* ED. F. DEGERING Purdue University, Lafaptte, Indiana
T
HE fervor for development during the past quarter of a century has manifested itself even in our educational institutions. The technic of teaching has undergone some noticeable changes. Some of the most marked of these advancements are t o be found in the field of primary education. As a specific illustration, brief consideration will be given t o improvements in the methods of teaching reading. In this particular branch of education there are three distinct stages of development, which, in the opinion of the writer, are observable. There is, first of all, the period in which the "ABC-method predominated. It is characterized by the emphasis which was placed upon individual symbols. The mastery of twenty-six isolated letters, with all their various sounds, was the basic requirement. This mastery, it was contended, enabled the beginner toadvance to the study of words and with a fair command of words he could hope to frame sentences. The basic concept of this method is illustrated by the following example:
but upon groups of letters or words that transmit broader concepts to the mind. I n the latest development along this line, primary emphasis is placed upou the sentence. It is recognized, at last, that the sentence is the avenue of expression. The beginner is taught, therefore, to concentrate on sentences. Smce words are the building blocks of the sentence, their meaning and use are acquired incidentally from correctly constructed sentences. Cousideration is then given to the individual letters as the building blocks of words. The basic concept of this method is iUustrated by the following revision of the previous examples:
Organic chemistry deals with the chemistry of the compounds of carbon.
The beneficial effect of this development in the teaching of reading is questioned, no doubt, by many. Only time can render the final verdict. The indications are, however, that an advance has been made in the right direction. If this be true, then consideration might be given to the application of these basic conIn this illustration the individual letters, which cepts to t h e teaching of other beginning subjects. convey little or no meaning, make their impression Should one use the "ABC-method," should he emupon the eye. Fifty-nine separate impressions must phasize specific cases, or should he place stress upon be segregated and grouped into words, and then ar- genera' concepts? In the teachmg of beginning organic chemistry, ranged into a sentence before one acquires a significant these three methods of approach may have their impression. This process of advancing from the specific counterpart. If the chemical properties of the alcohols to the general tends to stress the inductive method. In the next stage of development in the teaching of be selected as a specific example, the "ABC-method" reading, the emphasis was placed upon individual of presentation might be represented about as follows: words. Scores of words, with their individual meanings, were crowded into the mind of the beginner. I t ETHYL ALCOHOL REACTS WITH: was argued that words, and not letters, were the (I) Metallic sodium to give d i u methoxidc and hydrogen, essentials for adequate expression. With a large 2CHrCHrOH 2Na +2CHrCHrO.Na (sodium ethoxide) HZ: vocabulary at one's command, it was contended that (2) Hydrochloric acid, in the presence of a dehydrating agent, to the formulation of sentences would he comparatively give ethyl chloride and water, easy. The basic concept of this method may be CHVCHVOH HCI/H2S04+CHrCH2.U (ethyl chloride) HZSOIH~O: 'larified the fouowing revision of the (3) Acetyl chloride to give ethyl acelate and hydrochloricacid,
carbon the of chemistry with deals of compounds organic the chemistry. The Bty-nine characters of the previous example have taken the form of eleven words. One" attention is no longer focused on individual letters,
-
* Presented before the Division of Chemical Education at the ninetieth meeting of the A. C. S., Kansas City. Missouri, April, 1936.
392
+ + + + CHaCHrOH + CHrCOC1 +CH8.CO.O.CHrCH8 (ethyl acetate) + HC1:
(4) Chromic a i d to give acetaldehyde, sodium hydrogen sulfate, chromic sulfate, and water, 3CHrCHrOH NaCnO, 5H&%04+3CHp.CH0 2NaHS0, Crr(SO& 7H20: (5), Acetic on&dridc to give ethyl acetate and acetic acid, CHvCHrOH CH&O.O.OC-CKc + CHaCO.O.CHWCHI(ethyl acetate) CHSCO-OH: (6) Sulfuric acid to give ethyl hydrogen sulfatc a& water, 2HO.SOa-OH + CHvCH2.0.SOrOH CHrCHrOH (ethyl hydrogen sulfate) HL30vH10:
+ +
+
+ + +
+
+
+
(7) Ethyl hydropen sulfate to yield ethvl ether and rerenerate
+
+
HO SO1 0 C H 2 CH,, heatCH, CIIa CH2 OH CIb 0 CH1 C I t (ethyl ether) H?SOI: Arettc orrd. ?n rhe t ~ r m c oe f lrvdroeen ton ond a dehvdrottm
+
+
+
0
agent, to give ethyl k a l e an2 &ater; CHrCHrOH CHrCO.OH/HzSO4 --+ CHrCO.0.C H r C H s (ethyl acetate) H?S0,.H20: Phosphorlcs @entachloride to g w ethyl chloride, phosphorus oxychloride, and hydrogen chloride, PCI.--+ CHs.CHrC1 (ethyl chloride) CHSCHYOH POCI. ~. HCI: ---~ r i e n a r d reaent to eioe Uhozv mamesium halide and a . . " hydrocarbon,CHrCHrOH CHs.Mg.1CH&HrO.Mg.I (ethCHc: o x y magnesium iodide) (11) Hydrogen bromide to ginre ethyl bromide and vatcr, CHrCHrOH HBr.. d m (ethvl . +CHrCH,.Br . . . bromide) H20: (12) Phosphorus trichloride to give ethyl chlmide and phosphorous acid, ~ C H ~ C H T O HPC1. 43CIt.CH&!1 (ethyl chloride)
+
I , U.r.0.. -8.
+
+
+
+
+ + + +
.
+
.
(13) Sulfuric acid at 170°C. to give ethylene and water, C H a C H r O H f HO.SOrOH -+ CHsCHrO.SQ.OH (ethyl hydrogen sulfate) HsO, t h e n CHrCHcO.SOYOH, heat t o 170°C. -+H2C:CHs (ethylene) H.SO,: (14) Chrmnic a d d , in ezcesa, to give'acciic acid, sodium hydrogen sulfate, chromic s u w t e , and water, 2NarCr20?/101tS0,, aq. --t 3CHa3C14CHrOH 2Crz(S04)s l l H 1 0 . CO.OH (acetic acid) 4NaHSO4
+
+
+ +
+
+
Each of the precedingequationsmakes their individual impressions on the mind of the beginner in organic chemistry, but there is almost complete lack of correlation. Each equation must be mastered as an isolated fact. In the "word-method" of presentation, the same material might take a form somewhat as follows: ETHYL ALCOHOL REACTS UNDER PROPER CONDITIONS:
( 1 ) T o giue alkoxides when treated with actiwe metals. C H r C H r O . N a (sodium ethZ C H ~ C H Y O H 2NaHI: oxide) ( 2 ) T o give alkyl helides when treated with (a) dry hydrogen halides, (b) halogen acids in the presence of a dehydrating agent, (6) phosphorus pcntehalidcs, or ( d ) phosphorus trihalides, H B r , dry+CH..CHz.Br (ethyl (a) CHrCHzOH HnO: bromide) (b) CHvCHrOH HC1/HzSO,, aq. --t CHs.CH2.CI HSSOUHZO: (ethyl chloride) PCls-+ C H s C H n C l (ethyl chloride) (c) CHrCHrOH POCls HCI: (d) 3CHrCHrOH PCb+3C&CHrCI (ethyl chlorHsPOs. ide) ( 3 ) T o give esters when treated with (a) acid holidcs. (6) acids i s the bresence of ,hvdroeen . " ion and a dehvdratine- aeent. - . or fc) acid aniydrides, (a) CHrCHnOH C H r C O C l + CHs.CO.OCHrpH. lethvl acetate) HCI: ----(6) t- C I t C 0 . 0 H / H S 0 4 4 CHs.CO.H2SOrH20: 0 - C H r C H , (ethyl acetate) (c) CHs.CHz.OH CH8.C0.C1,OCCHs -+ C I t C 0 . ~nr~v-vn. O.CH1-CH, (ethyl acetate) ( 4 ) T o give ( a ) ethyl hydrogen sulfates when treated with sulfuric acid at room temperature, (b) dhers when treated with sulfuric acid and additional alcohol at about 140°C., or (c) olqins when trmted with sulfuricacid and heated lo about 1709C., ( a ) CH&HvOH 2H0.SOrOH, cold 4 CHrCHrHSSOKHBO,t h e n 0 - S O 1OH (ethyl hydrogen sulfate) (b) C H r C H v O H C H r C H 2 . 0 6 0 a . 0 H . 14O'C. -+ CH8.CHr0.CHyCH8 (ethyl ether) H I S O C H ~ O ,or (6) CHs.CHrO.SOrOH, heat t o 1709C. 4 H3C:CHZ HsSOa. (ethylene) . . . deperulinl: on the condilionr. oriJolion products o r (5) To ( 0 ) aldehydes, ( b ) 062s. ( c ) other o x d i z d dcri~attvrr,nr ( d ) cleatngr uhrn trmlpd yilh npp~opriot? r i . i i 2 i q q e n l s .
+
+
+ +
++ + + + + +
..
+ +
CE.CH~OH \----,-
+
+
,,.+ ,..-?.-
+ +
+
+
+
,
+ ++
+
( a ) 3CHwCHvOH Cr&H z 0 + 3CH&HO 2Crt++ SOH-: (b) 3 C H v C H r O H 2CrrO?5Hn0 --t 3CHn.CO.OH 4Crt++ 160H-: (c) CHrCHwOH 6HNOa +H O C H y C O . O H (gly6N01 4Hz0. c o l ~acld) ~ Subsequent midation yields H.OC.CO.OH and HO.OCCO.OH, t h e n ( d ) 5HO.OC.CO.OH 2MnOa-, aq. +10C0, 2Mn++ 2Hn0 60H-.
+
+
+
+
+
+
By this method of attack, the twelve isolated equations of the previous example have been grouped under five general headings according to the general nature of the products formed by the reaction. A further extension of the technic of teaching heginning organic chemistry, corresponding to the "sentence method," might permit arrangement of the same material in a tabulation like the following: THE MONOAYDROXY ALCOHOLS REACT UNDER PROPER CONDITIONS:
1. B y replacement of (@) the hydrogen a t m of the hydroryl group, or (b) the hydroxyl group, as indicated bclmo when treated with: ( a ) 1. Active metals R.0 H Na alkoxides 2. Acid halides R.0 H X 0 C . R esters 3 . Organic acidsf- R.0 H H O 0 C . R esters (HZSO., etc.) R.0 H R.CO.0 0 C . R esters 4. Organic acid anhydrides 5. Alkyl hydrogen R.0 H HOSOIO R ethers sulfates R.0 H 6. Grianard reR MaXalkoxvcoma p e i t , etc. 2Na 4 pounds, or more specifically, 2CHrOH CH2.0.Na (sodium rnethoxide) Ha. HI1 alkyl iodides Hydriot lic acid/- RJOH (red phc ,sphorus) H Br alkyl bromides Hydrogt ?n bromide R OH (or HC1), dry lloric acid R OH H Cl alkyl chlorides Hy*l I nG r i i x ) / H Z S O 4 - dfuric acid, room R OH H 0 . S 0 2 . 0 H alkyl H temperature sulfates Phosphorus tri- 3 R OH P Cls alkyl chlorides halides I 6. Phosphorus pentaalkyl halides, halides or t o illustrate, C H r C H r O H H I / ( P ) , heat -+ CHVCHYI (ethyl iodide) HzO. 2. B y dehydration, to give unsaturated deriwatiues, T h e ease o f dehydration in- Z creases i n t h e order R C H c : OH. R I C H . O H , R G O H A s a n example, C H a C H r . O H PnOs, heat -+ H2C:CHe (ethylene) 2HPOs. 3. B y ozidation, with appropriate reagents, as indicated below. a ) R C H Y O H +R C H O -+ R C O OH + ( primary alcohol aldehyde acid oxidized derivative --+ cleavage: + RnC:O 4 oxidized derivative (b) &CH.OH
+ ++
I
1
+
1
+ +
I
+
+
+
+
+
+ + R~OIH+P&~ + +
~
1
+
+
secondary almhol
+cleavage:
'
ketone
+oxidized derivative 4 cleavage: (c) R,C.OH I n t h e case o f ethyl alcohol, CHrCHYOH ----t CH&HO -+ CH,.CO.OH --t '
ethyl aleohol
HO.CH,.CO.OH glycolie acid
acetaldehyde
HO.OCCO.OH 4 C01 oaelie acid
aeehe acxd
4 H.OC.CO.OH --t glgoxylic acid
+ HnO
In this illustration, an entire group of reactions is visualized in much the same way that the eye scans a group of words to discern the meaning of a sentence. Obviously, this method of teaching chemical reactions to beginners in organic chemistry has certain distinct advantages. These correlations have served to indicate that
organic chemistry, like reading and other subjects, may be taught in distinctly different ways, depending in each case on the viewpoint of the instructor. The individual instructor must, in the last analysis, decide for himself whether he wiU place primary emphasis upon (a) the individual compounds, (b) the types of compounds, or (6) the types of reactions involved.
