Introduction to Practical Chemistry III, Chemistry tutorial

Introduction:

Research training in the preparatory inorganic chemistry must instill self-confidence derived from the capability to handle substances by diverse properties, example: reactive gases, volatile and pyrophoric reagents, moisture-sensitive compounds and refractory solids. Scholar laboratory classes offer the basics of synthetic chemistry, however time and resource limitations confine the treatment of more advanced methods or procedures. Final year undergraduate project in a research laboratory might offer first-hand experience of more complicated experimental techniques though, again, time is frequently limited.

This introduction has been written to bridge the gap between teaching and research atmospheres, to assist new research students finding their feet in the laboratory, and to introduce methods for conducting air-sensitive compounds. Practical chemistry is essentially a very personal experience and which tried to join coverage of the fundamental methods with an explanation of selected, more specialized methods (comprising some which encompass only recently been adopted through inorganic chemists) in an effort to give beginners and non-specialists by the confidence to tackle the kind of preparatory work they are probable to encounter in the literature.

However specific streams of chemistry are not covered in detail, the methods illustrated are usually applicable to reactions comprising air-sensitive compounds. Likewise, the discussion of spectroscopic methods is limited to the practical features, and appropriate references are given where more detailed information might be needed.

The laboratory:

For a graduate student joining a research or practical laboratory group there is generally an initial feeling of strangeness in the unfamiliar laboratory, and even postdoctoral researchers who have worked in the area and who encompass some knowledge or experience of the general apparatus and methods take a while to adapt to latest surroundings. This is worth remembering while you search each and every cupboard and drawer in the lab for that one specific item of glassware or apparatus you require setting up your first reaction. Do not hesitate to ask established post grad or postdoc co-workers (or even your administrator) concerning the organization of the lab and the department.

Research groups evolve somewhat different protocols for the daily routine, however the necessary elements are common to all such engaged in synthetic work and, for the aims of this discussion, we will discuss different methods in some detail, however our main purpose is to provide an overview and comment on general features of the lab management.

Bench space:

Most of the work that will be carried out in what you will come to regard as your own bench space or in the fume cupboard. Around the lab there will as well be communal bench space for shared equipment, and the quantity of space allocated to you will clearly based on the number of people in the lab and the quantity of communal equipment. These days, it is standard practice to perform preparative metal organic reactions in an inert atmosphere in such a way that we will require the essential facilities at your bench in order that oxygen and moisture can be regularly excluded from reactions. Bigger, permanent items of glassware are best supported on the lattice frame-work of metal or fiberglass rods that is fixed firmly to the bench and/or a wall. However construction is quite straight-forward, some characteristics can make life at the bench simpler and these must be borne in mind from the outset. For electrical safety, a metal frame-work must be joined to an earth point. The rods must be positioned so as not to block access to electrical sockets and switches or to gas taps and shelves placed behind the frame-work. Feet securing the rods to the bench top must be as small as possible and the circular, three-hole kinds can be sawn down for attachment via a single screw. Horizontal rods are comprised mostly to impart rigidity to the frame-work; the weight of any items clamped to such rods can cause the clamps to rotate downwards. Apparatus must, thus, be clamped to the vertical rods that can be arranged easily across the working area and be of adequate height to support permanent items like gas purification columns and vacuum manifolds that require to be positioned so as not to block your work at the bench. Always try to arrange the bench top in such a way that it is simple to keep clean and tidy and so that apparatus can be employed with the minimum of movement on your part. If likely, a separate area of desk space must be available where you can write up your lab book and keep spectra and other paper-work.

Fume cupboards:

In a perfect world, all the reactions would be carried out in proficient fume cupboards, however financial and space restrictions signify that in scholastic labs these are normally shared, thus reactions comprising less dangerous substances are often taken out at the bench. This doesn't generally pose any problems whenever carrying out reactions in a controlled environment, as the main purpose is to protect reagents from the atmosphere, which deals with the safety considerations. Fume cupboard performance must be examined regularly by utilizing a rotating-vane anemometer and the details recorded in a note-book. The cotton threads or a piece of tissue paper taped to the lower edge of the sash give a permanent visual indication of the air-flow. Note that a reduction in an efficiency or even fan failure can outcome if employed pieces of paper towel, aluminium foil or cotton wool are drawn to the extract system so, as a subject of routine, these must for all time be eliminated from the fume cupboards.

Apparatus and glassware:

The details of glassware and apparatus for routine use will probably attain your own personal collection, however much will be communal and a certain amount of discipline is needed from everybody in the lab to keep shared equipment clean and in good condition. The high-vacuum line will almost certainly be shared, as will more often employed equipment like dry boxes, fridges, ovens, freezers and balances. Daily electrical items like stirrers, heater/stirrers, heating mantles and hot air blowers (that is, of the hair dryer or paint-stripper kind) require to be maintained in a good working order and checked frequently for frayed, worn or melted cables.

Solvent stills:

Dry, oxygen-free solvents are required for most reactions, and communal solvent stills are generally set up in the lab for the generally used solvents. To function appropriately, stills require frequent attention and maintenance and are a potential source of friction in the group. It is everybody's responsibility to make sure the right use and proper maintenance of the stills and one good way to accomplish this is to organize a rota for cleaning and regeneration.

Procuring chemicals and equipment:

From time to time, we will find out that some of the chemicals or items of glassware are not obtainable in the lab and you will require knowing how to purchase new supplies. This is generally done centrally in a department and, after recognizing an appropriate supplier, we will probably encompass to fill out an order form and hand it to somebody in the stores. This must be done in consultation by your supervisor, firstly to make sure that funds are available, and secondly to check that the disposal methods for all residues and unused chemicals can be followed, as this can frequently cost more than the chemicals themselves.

Carrying out reactions:

The details of each experiment must for all time be planned cautiously and it often assists to sketch apparatus before assembling it. Try to perform the experiment mentally first, so that you can imagine each and every step and predict any potential problems or troubles with material transfer or manipulation. Synthetic chemistry is an art, and synthetic chemists are generally judged by their capability to select suitable reagents and reaction conditions for the preparation of latest compounds. Talk to most people who have been in the game for some time and we will find out that they are all in it for the similar reason - they enjoy making latest compounds, and it is frequently this enthusiasm which differentiates the outstanding research worker from the rest. As you put on confidence and become more known with the methods, setting up the glassware for reactions will become second nature to you, however you must never let yourself to become satisfied. Carrying out a reaction is frequently the simplest portion of synthetic work. Much more effort is generally comprised in the work-up, that is, the separation and purification of the different products, and in the following characterization of compounds obtained, and you must be prepared for a good measure of frustration as you tackle such basic challenges. Your reward for all your efforts will in the major part be the sense of elation that accompanies success.

Cleaning and drying glassware:

This is an extremely significant part of lab work and it is necessary that you are capable to do it correctly as there isn't much point in utilizing dirty glassware for your reactions. A poor performance in this area whenever it comes to shared apparatus is probable to upset other group members, therefore it is best to get it right from the starting! After rinsing by an organic solvent like acetone or industrial ethanol (that is, methylated spirits), flasks can be washed carefully with hot water and detergent by using a test-tube brush to take away solids from the glass surface. Stubborn residues can generally be eradicated with care by using concentrated nitric acid (make sure that no alcohol remains in the flask, or else the vigorous reaction might spray acid to your face) or alkaline peroxide solution (that is, for early transition-metal oxide residues). Chromic acid baths have traditionally been employed to take away organic residues, however these are best avoided as chromium salts are now listed as carcinogens and they can as well destroy necessary bacteria in water treatment plants. In certain cases, an ethanolic KOH bath can be employed to soak glassware overnight. This will assist to take away residual silicone greases, however items must not be left in the bath for too long, as the glass will steadily dissolve and become weakened (particularly harmful for glassware that is to be emptied). This applies particularly to sintered glass filters and to ground-glass joints and taps.

Once the glassware is clean it can be dried in the oven at 120 to 150°C. It is beneficial if you are to be working by moisture-sensitive compounds to make use of ethanol (that is, industrial meths) for the final rinse as it forms an azeotrope with water that assists to take away residual moisture. Dry glassware must then be assembled rapidly whereas hot (wear protective gloves) and allowed to cool under vacuum to minimize the exposure to atmospheric moisture. Whenever the glassware is not to be employed for a while, it must be stored in a cupboard or drawer and protected from impact by round-bottom flasks, which tend to roll around and cause 'star' cracks if drawers are opened and closed too strongly. It is, thus, a good idea to line drawers by cotton wool or a thin layer of foam packing that can be fixed to the bottom of the drawer by double-sided adhesive tape.

Disposal of residues:

In the UK, anybody using chemicals, whether in university or industry, has a legal responsibility to make sure that all the waste is disposed of safely. Whenever planning experiments, the final fate of all solvents, reagents and products should be borne in mind from the outset and a safe means of their disposal should be available. Only non-toxic aqueous wastes must be poured down lab sinks. Acids and bases must be highly diluted, and it is best to avoid disposing of any organic solvent down the sink, however small amounts of alcohol from the washing of glassware pose no hazard whenever diluted with water. Organic solvent residues must be collected and given to a registered waste disposal company whose advice will find out which residues can be combined. Acetone can be recycled if it has been employed only for rinsing cleaned glassware and can, thus, be collected separately. Though, solvents used in reactions will be contaminated by a broad variety of other materials and can't be recycled and will perhaps be incinerated. Chlorinated solvents need high temperature incineration and require to be collected separately all along by any mixed solvents in which they are present. Flammable non-chlorinated solvents are frequently employed as fuel for incinerators and can be collected altogether. Any particularly toxic solvents must be collected separately and labeled suitably prior to disposal. At all times, it is necessary to take precautions to avoid the generation of potentially reactive mixtures and, if you are in any qualm store the residues separately and label them correctly.

The literature:

The primary step of any research project must for all time be a literature search. You require being aware of the background to the project, recognizing others working on the same or associated topics and establishing the present state of knowledge in the area. Regular visits to the library must become part of your routine so you can stay side by side of any developments by scanning present journals and reviews. This will take a little time to identify which journals are probable to have material most relevant to your work, however once this has been established these will form the base for your regular visits to the present periodicals part of the library. The simplest way to determine which journals to look at and where to discover them is to ask your colleagues; they will have already been through this method and accumulated their own expert knowledge. Moreover to the 'main-line' journals, there are those of a more general, applied or interdisciplinary nature and we will most likely as well want to maintain an awareness of most important developments in other streams of chemistry.

Keeping records:

The significance of recording details of literature searches and of forming a systematic procedure of storing the information obtained has been emphasized above. Precisely the similar principles apply to the experimental work. Correct details of each and every experiment must be recorded in a hard-backed notebook and they must be adequate to enable you or someone else to repeat the work. Products must be labeled visibly to recognize them with a specific experiment, and stored in such a way that they can simply be found in the future. Associated spectra and other data must be clearly labeled to recognize them by particular products of any experiment and then filed in a systematic fashion to let ready retrieval. This level of discipline is necessary for successful synthetic work and anything less comprises a sloppy approach. Various groups develop their own styles for recording their work however some significant characteristics must be common to them all.

Safety:

The chemical laboratory can be a harmful place to work, however this doesn't necessarily mean that it is hazardous. A well-organized and well-managed lab is probable to be safe and pose minimal risks to health. Each and every substance or operation has a related hazard - a potential to cause harm. The likelihood that harm will in fact be caused is the risk related by any process. It follows that to work safely you should:

a) Recognize hazards related by all substances and methods you intend to use;

b) Minimize the probability that any harm will be caused by such combined factors.

What follows is a summary of the significant points of laboratory safety. No list of guidance can cover all eventualities, and we will be needed to read the department's own safety booklet whenever we start so, in addition to emphasizing the fundamentals.

General behavior and awareness:

Common-sense must prevail while you are in the laboratory, which signifies adhering to some straightforward codes of conduct.

a) Always be dressed in safety spectacles.

b) Do not eat, drink or smoke in the laboratory and do not work after drinking alcohol.

c) Work cautiously, do not rush anything and do not become self-satisfied.

d) Ignore working alone, someone in earshot should be aware of your presence.

Moreover, you must for all time be prepared for any emergencies or accidents. Every so often, ask yourself, 'What would I do if something occurs now?' If you are uncertain of the answer, you must not be working in the lab.

  • Be familiar with the location of eye washes and/or safety shower.
  • Be familiar with the emergency exit routes, the evacuation method and the alarm sound.
  • Be familiar with the location of fire-fighting apparatus and how to utilize it.
  • Be familiar with how to summon help (like first-aid, ambulance, fire service and so on).

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