mfety in the chernkol loborotory
edited by
MALCOLMM. RENFREW University of Idaho Moscow, Idaho 83843
Flameless Organic Teaching Laboratories are Safer F r e d e r i c k J. M a t h e w s Laboratory Craftsmen Inc., P.O. Box 148, Beloit, WI 5351 1
A timely goal of many colleges is to make the lahoratorv eomoletelv flameless hv the use of rlrctrir hentmg equipment. Steam heating, uudoubtrdly rhe safest, x h d d be used wherever possible in those laboratories fortunate enough t o have it; distillation and refluxing procedures requiring temperatures above 100°C can then he supplemented with electric heating. Colleges have lagged far behind industrv in revlacine the Bunsen hurner with electric heat for several reasons. ~
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the threat of law suits resulting from personal injury seems t o be hastening the advent of the flameless laboratory. Suitable equipment is available now for a practical, economically feasible. flameless oreanic teachine laboratory t his equipmentls durable, oikmd design, 1'L or CSA listrd trrqutred in srme Rtntei and cities),and 50me of i t is rplativelv law in cost. Round-bottom flasks may be heated with a durable flask heater (heating mantle) with a design that will permit a given flask heater to be used with undersized flasks. For examule a 50.1111 flask and contents can be heitad effectively m a 100-ml flask heater by the air-bath technique. This is an important budgetary consideration, since by this technique it is possible to heat all four or five flasks in a standard glassware kit (essential eauioment) with only two flask heaters. Thus a 500-ml flask heater can be used to heat the 500-ml and 250-ml flasks, and the 100-ml flask heater will handle the 100-, 50-, and 25-ml flasks. Inability of readily available flask heaters to make use of the air-bath technique in the past has been s big deterrent in achieving a flameless all-electric student organic laboratory.
Fmderlck J. Mathews recewed his RID m organlc chsm,slry from lhe Un verslty a1 Wisconsin (Madison).He was involved in indusbial r w c h wit+ Rohm 8 HaasCa. for three years during World War 11. He taught chemisby fa a year at Kent SWe Univwsity and at Beloit Colleoe for 12 vears. In 1953 he eslaoltshea atmatory Cratrsmen lnc. IBelool. WII, and he is now president 01 the firm.
Electric flask heaters (mantles) that are capable of being used for air-bath heating are those constructed with either a quartz fabric (Glas-Col Corp.), a high-alumina fabric (Briscoe Mfg. Co.), or the ceramic-type heating cavity with the resistance wire completely embedded (Laboratory Craftsmen Inc.). Glass fabric mantles tend t o superheat when used with undersized flasks, which causes the fiberelass sleevine " surroundine the resktance wire L O melt and hreak off. The other types mentioned a t w e ran withitnnd much higher temperatures without damage to the heating unit. The ceramic-type heatem are far less porous than the fahric types and will contain the contents of a broken flask for a much longer time. Also, solvents and chemicals aceidentallv suilled into a ceramic-typp hratinr: cavity will not prnrtratr nearly as far in a given time period as they w~llwith the falriv-type unita.
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Other Important Electrical Accessorles Some other electric heating accessories important to the flameless organic laboratory are: 1) Melting point apparatus. Several are available such as the Kofler hot stage, the Thomas-Hoover Uni Melt, and Mel-Temp (Laboratory Devices) to name a few. One for every three t o six students should he sufficient. 2) A low wattage hot plate that can heat small quantities of a liquid in a heaker or test tube (see below). Hot plates with a power consumption in excess of 300 w can easily overload laboratory circuits, especially when electric flask heaters are also being used. Two small hot plates are now available from Thermolyne Corp. (300 w) and Laboratory Craftsmen Inc. (200 w). 3) The heating of liquids in test tubes (150 mm long) is now possible by use of the Test Tube Heater Block (Cat. No. TTHB, size B, Laboratory Craftsmen In&). The TTHB is an aluminum block 1.5 in. in diameter by 1.0 in. hieh with s hole bored throueh " it laree enough toaccept a 150-mrn trst tuhr. When thr'I'THH is placed on a hot plate at a muderate temperature, 3 ml of water can be brought to a boil in less than 3 min. Smaller test tubes can also be used with the TTHB. 4) Boiling point determinations witb as little as 4 ml of a liquid, boiling in a range Volume 62
from 50' to 230°C (for unknowns or testing for purity) can be made with electric heat, using a small hot plate, a TTHB (size B) aluminum block, and several other easily acquired accessories. The technique was developed by Laboratory Craftsmen Inc. in 1983. So, all the essential devices and equipment needed for producing a flameless, all-electric organic teaching laboratory are easily available a t moderate cost. The Bunsen burner can,then, finally be retired from the organic laboratory. Benefits of Eliminating t h e Bunsen Burner To what extent are the hazards in a laboratory reduced, and the benefits increased, by eliminating the Bunsen burner? Heating everything electrically by no means eliminates all hazards associated with the heating of flammable liquids as is required in an arganic laboratory. However, electric heating in a student orzanic laboratory with goad rqui[,mtnr and g o d wpprvlslon will: 1I Eliminate porstblp cerious firrs arising when hot llammahlr lmuidsarp hand.pd near an open flame. Quite often the cause of laboratory fires has been the burner of the student "next door" which was pushed too far to the right or left and was not noticed by the adjacent student preoccupied with the pouring of the hot or cold liquid from one vessel t o another. 2) Increase substantially the control of chemical procedures such as distillations, digestions, refluxing, etc. This is because the heating is much more uniform over the flask bottom (reduces superheated spots), and very small changes in power either up or down are easily effected witb a good power control device. Dependable low-east power controls are also now available. 3) Permit the use of smaller quantities of materials in laboratory experiments by going from the macro scale to the semimacro scale. Fractional distillations of as little as 10 ml of a liquid are possible with electric heating, but not with the Bunsen burner. Smaller portions of a flammable liquid in an experiment means smaller and better cotnained fires, should one occur.
(Continued on page A441 Number 2
February 1 9 8 5
A43
4) Make for better separations in distillations because of the enhanced control. 5) Eliminate the annoying but not-sodangerous fires that Bunsen burnen cause. Such fires result when a burner is placed too close to the edge of the hench top and shirt sleeves or aprons catch fire or long hair is singed, or when the burner is knocked off the bench, burning garments or the burner hose. In older bench setups burners sometimes are accidentally pushed under the wood reagent shelf that runs lengthwise down the center of the laboratory bench, with the student oblivious to the smoldering shelf.
Hazards Remalning in Flameless Laboratories Fires in flameless laboratories are still possible if one carelessly uses and handles solvents (liquids) with low auto-ignition tpmoeratures. All flammable liouids have an -~ auttr-ignitim temperature. Thii is thr temperature at which the liquid's vapor, when mrxtd with the correct amount of air, will ignite spontaneously upon contact with a hot object such as a hot plate, heating mantle, flask heater. oil bath. or hot ring. Among t& common laborat& solvents, diethyl ether has, by a wide margin, thelowest auto-ignition temperature (185'C); ether fumes should not be generated around hot objects unless there is excellent ventilation. Procedures that require removal of ether (from extractions) by open boiling or rapid evaporation must be done with great care and with adequate ventilation. It is recommended that ether and other low boilers be removed by distillation using a condenser. If evaporation of ether or petroleum ether must be done by open boiling, do not use an undersize flask in a flask heater. Select a flask that completely tills the heater cnvity, and use low settings. The table lists auto-ignition temperatures of some common solvents and gases. ~
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evaporated, some liquids leave peroxides or other heat-sensitive residues. When a flask hails dry at a medium power setting, the temperature of the bottom of the dry flask can quickly rise 100°C or more in afew minutes, and a s m d explosion can result from the decomposing residues. Or, if a little liquid condensate from the column then drips back onto a dry, hot flask bottom, at or above the auto-ignition temperature of the liquid, the liauid can ienite causine an exolosion. FIR?^ he& should be oper&d abovc the bench t ~ , plevel ar all rlma, using a ring stand w ~ t hrhr heating unit properly iupportrd bv a ring with a metal plate support or the special ring for mantles. This permits a cooleroperating heating unit and also permits the flask heater to be lowered quickly from the flask in case a chemical reaction is exothermic and seems to be getting out of control. Design Standards-Laboratory
Liability Each year more states (and Canadian provinces) require UL (Underwriter Laboratory) or CSA (Canadian Standards Association) listing or certification. A product listed with either of these two evaluating agencies means that the electrical design and the construction (as it affects the electrical desieu) .. . of the oroduct conform to rieid stanaards, w h ~ &warantees h maximum s&ty from rlrrtr~c~alshock 10 the person using the product. The agencies also mmitor thc manufacturing process to he sure design conformity is maintained. The question of liability in the student laboratory, when an accident does occur, oresentlv seems to be in limbo. The soate of Inw s u m that drveloped 5 to 10 y e w s ago has lcssen~dm the last few yenm OSHA haidone much to enwurage ~mpruved satety of working environments of employees in industry. However, OSHA's jurisdiction in academic laboratories appliesonly to employees, not to students. This apparent regulatory void may explain the considerable lag in safety practices and procedures in many academic laboratories. However, a new awareness of the need for Less hazardous laboratory environments is developiong rapidly, and many college laboratories are taking this challenge seriously. For maximum liability protection against laboratory accidents, it is clear that good equipment in good working condition, goad supervision, and the proper preparation of the student are essential. Alan Hutchcroft of Rockford College (Rockford, IL) is among those who have pioneered in developing an all-electric organic Laboratory. He has said that for the last 15 years, during whieh essentiallyall heating was done in their oreanic laboratories electricallv. , rhry have managed In a w d laboratory fires "WPhave relegntcd fhr Hunwn burner to ure in the h w d for one or twu experlmrn- n ~
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Auto-lgnlflon Temperatures (OC) Diethyl elbr Petroleum emw, b.p. 30-60 Ligroin. b.p. 60-90 Ligoin, b.p. 90-
185 230
Methanol Ethyl acetate
465 480
230 230
Propane Acetone
465 575
250 425
Benzene Hydmgen
580 580
120
Kerosene Emanol
Another hazard in all laboratories involves distillation to a dry-flask condition. When
A44
Journal
of Chemical Education
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There are mans ncndemic tsboraror~esm both t h United ~ Stawsand ('anada that now do nll of their round-bottom flask heatme electricallv in their student areanic laboratories With more laborntorier each yrar brcoming all.electrir, the flnmeless laboratory is well ratnhlished. It is m,nomicnlly fmihlr. it makes the laboratory a safer and better place in which to work, and it adds to the efficiency of laboratory proeedures. I t is here
