3
32
G. CHUCHANI ET AL.
Step 1 is a fast process of dehydrochlorination. The ester
calculated from the pressure increase manometrically, or
by the quantitative chromatographic analyses of ethylene
product. The temperature was controlled by a Shinko DC-
PS resistance thermometer controller and an Omega
SSR280A45 solid-state relay, maintained ꢁ0.28C and
measured with a calibrated Iron Constantan thermo-
couple. No temperature gradient was observed along the
reaction vessel. The starting materials, dissolved in
benzyl alcohol or acetic acid, were all injected directly
into the reaction vessel with a syringe through a silicone
rubber septum. The amount of substrate used for each
reaction was ꢅ0.05–0.2 ml.
intermediate proceeds through a slow determining Step 2
for the formation of the corresponding a-amino acid and
ethylene gas. The ‘in situ’ unstable amino acid from Step 2
rapidly decarboxylates to the corresponding amine
(Step 3). Ethyl ester of sarcosine is the exception since
only produces the corresponding amino acid. These results
10–12
apparently support the consideration reported before
where a-amino acids decarboxylate to the corresponding
amines. It is interesting to report that phenylalanine was
15
found to decompose in a stainless steel reactor, between
4
00–6008C from 4 sec to 1 min, with complex results.
The general concept that electron-withdrawing groups
at the acid side of ethyl, isopropyl, and tert-butyl esters
enhance the elimination rate, while electron-releasing
groups reduce it has been described in a review on the
16
structural effect on gas-phase reactivities. However, the
comparative rates of the gas phase reactivity of the ethyl
esters of amino acid hydrochlorides listed in Table 7 seem
to be contrary to the above-mentioned generalization.
Steric accelerations appear to influence the process of
decomposition. That is, the bigger the size or the more
bulky is the substituent at the acyl side of the amino ester,
the faster is the elimination rate of ethylene formation.
REFERENCES
1. Taylor R. The Chemistry of Functional Group. Acid Derivatives,
Supplementary, vol. B, Saul Patai (ed). Wiley: London, 1979;
Chapter 15.
. Holbrook KA. The Chemistry of Acid Derivatives. Vapor and Gas
phase Reaction of Carboxylic Acids and their Derivatives, vol. 2,
Saul Patai (ed). Wiley: London, 1992; Chapter 12.
2
3
4
5
. Al-Awadi NA, Kaul K, El-Dosouqui OME. J. Phys. Org. Chem.
2
000; 13: 499–504.
. Safont VS, Moliner V, Andres J, Domingo LR. J. Phys. Chem. A
997; 101: 1859–1865.
. Domingo LR, Andres J, Moliner V, Safont VS. J. Am. Chem. Soc.
997; 119: 6415–6422.
1
EXPERIMENTAL
1
Glycine ethyl ester hydrochloride (Aldrich), sarcosine
ethyl ester hydrochloride (Aldrich), DL-alanine ethyl ester
hydrochloride (Aldrich), and L-phenylalanine ester
hydrochloride (Aldrich) of 99% purity were employed
6. Domingo LR, Pitcher MT, Andres J, Moliner V, Safont VS,
Chuchani G. Chem. Phys. Lett. 1997; 274: 422–428.
7
. Domingo LR, Pitcher MT, Safont V, Andres J, Chuchani G.
J. Phys. Chem. A. 1999; 103: 3935–3943.
8. Rotinov A, Chuchani G, Andres J, Domingo LR, Safont VS. Chem.
Phys. 1999; 246: 1–12.
(
GC-MS: Saturn 2000, Varian, with a DB-5MS capillary
9
. Chuchani G, Dom ´ı nguez RM, Rotinov A, Mart ´ı n I. J. Phys. Org.
Chem. 1999; 12: 612–618.
column 30 m ꢄ 0.25 mm. i.d., 0.25 mm film thickness).
The products sarcosine, the hydrochloride salts of
methylamine, ethylamine, and phenethylamine collected
out of the reaction vessel were identified in a GC-MS
10. Ensuncho A, Lafont J, Rotinov A, Dom ´ı nguez RM, Herize A,
Quijano J, Chuchani G. Int. J. Chem. Kinet. 2001; 33: 465–471,
and references cited therein.
1. Lafont J, Ensuncho A, Dom ´ı nguez RM, Rotinov A, Herize A,
Quijano J, Chuchani G. J. Phys. Org. Chem. 2003; 16: 84–88.
2. Dominguez RM, Tosta M, Chuchani G. J. Phys. Org. Chem. 2003;
1
1
1
1
1
1
(
Saturn 2000, Varian) with a DB-5MS capillary column
0 m ꢄ 0.25 mm. i.d., 0.25 mm. The identification of
ethylene and carbon dioxide were performed GC-MS
Saturn 2000, Varian) with megabore capillary column
3
1
6: 869–874.
3. Al-Awadi SA, Abdallah MR, Hasan MA, Al-Awadi NA. Tetra-
hedron 2004; 60: 3045–3049.
4. Rosas F, Monsalbe A, Tosta M, Herize A, Dominguez RM, Brusco
D, Chuchani G. Int. J. Chem. Kinet. 2005; 37: 383–389.
5. Shulman GP, Simmonds PG. Chem. Commun. 1968, 1040–
1042.
6. Chuchani G, Mishima M, Notario R, Abboud JL. Structural Effect
on Gas-Phase Reactivities. Advances in Quantitative Structure-
Property Relationship, vol. 2, Charton M, Charton BI (eds).
JAI Press, Inc.: Stamford, Connecticut, USA, 1999.
7. Maccoll A. J. Chem. Soc. 1955: 965–973.
8. Swinbourne ES. Aust. J. Chem. 1958; 11: 314–330.
9. Dominguez RM, Herize A, Rotinov A, Alvarez-Aular A, Visbal G,
Chuchani G. J. Phys. Org Chem. 2004: 17: 399–408.
(
GS-Q 30 m, i.d. 0.53 mm with a TCD. The quantitative
analysis of the product ethylene (Matheson) was carried
out by using a Gas Chromatograph HP 5710A with a
Porapak Q (80-100 mesh) column.
Kinetics
1
1
1
The kinetic experiments were performed in a static
The rate coefficients were
17–19
reaction system reported.
Copyright # 2006 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2006; 19: 326–332