DJF90
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Glassware questions
At the moment I am trying to intelligently decide which pieces of glassware I should purchase (I want a new ground glass setup  ), however there are a couple of things I would like to know:
Joint size: I would like to be able to prepare stock reagents, and experiment on a small scale, and if possible do it all with the same bit of kit. Am
I right in thinking that 19/26 joints are what I need? The flask sizes vary from 25ml all the way to 1L and so should cover all of my needs, and also
for small scale stuff, pear shaped flasks are available in both 50ml and 100ml sizes (as these allow distillation to a very small volume). I have a
24/29 setup at the moment, but I think the joints are too big and there would be too much hold up on a small scale (I haven't been able to use it yet
due to a lack of workspace - also it has flat bottomed flasks (not erlenmeyers, but round shaped with a flat section). I want to sell this setup on
ebay, has a coil condenser too).
Condenser: I am aware that a simple liebig condenser will probably suffice but I like the look of a jacketed coil condenser It has a large surface area and so should be able to cope with any volatiles I could
throw at it. Is there any disadvantages to this type of condenser? Am I correct in thinking that to distil very high boiling compounds at atmospheric
pressure I can use this condenser, but not run any water through it?
Fractionation column: This is where it gets tricky... After searching the internet fairly extensively I can find no comparison of columns. I am aware
that a vigreux is not very good, and so I have to decide between the following options;
- Dufton column: Available in either 150mm or 300mm effective length with 19/26 joints. The spiral forces the vapor around a helter skelter pathway.
This is the cheaper of the two options (between £50 and £70).
- Pear bulb column: Comes as a 225mm effective length column, which is precision bored (like the dufton). However the pears and bulbs must be
purchased seperately, and the column requires 12 of each... bringing the grand total to just over £200 :O. However I believe this column to have
superior seperation . The other drawback is that the cone is 24/29 and the
socket is 34/35, and so I would also need to purchase the adaptors to make this fit with the 19/26 joints (I could also use these adaptors with a 60ml
soxhlet extractor if I was so inclined to buy one  ).
Addition funnel: I am opting for a pressure equalising funnel with rotoflo teflon stopcock. Capacity is 100ml, joint size is 19/26. Is the pressure
equalising worth the extra cash over a normal funnel? I will be intending to do work with vacuum and so I will probably be buying one at some point.
Separatory funnel (plain stem): Here I am stuck once again (possible even more tricky that the fractionation column...). What size should I get? In
19/26 joint the options are 50ml, 100ml and 500ml, however I could get a 24/29 funnel in 250ml size. Generally speaking I would hope to be working
with 50/100/250ml reaction flasks for the small scale stuff, 500ml and 1L for preparing reagents. So which size do you think I need?
Flasks: I was thinking 50ml and 100ml pear shaped, 100ml, 250ml, 500ml, and 1L RB, and a 3 neck 250ml flask for those complicated syntheses. I don't
think I would want to work in a smaller scale that with 100ml flasks, but I'll get the 50ml pear just in case 
As you can probably tell this is going to set me back a fair sum of money  however
chemistry is what I love and do best, and with a little bit of luck I'll be off to oxford university this october (I have an offer but I need AAA in
my A-levels). I'm working all summer on minimum wage (£4.60 an hour!!) to try and fund my extra curricular experimentation
Any comments/suggestions on my choices (or lack of decision) are welcome Thank
you all in advance
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kilowatt
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Joint size: 24/40 is definitely the way to go. It is the most common size, which means components are the easiest to find. Also 24/40 glassware
ranges from some of the smallest to some of the largest boiling flasks etc. You can get 50mL or 12,000mL flasks that have 24/40, and all manners of
adapters.
Condenser: A liebig condenser is indeed suitable for most stuff, you'd be surprised. I have a couple one-piece distillation heads that have vacuum
and reflux control, and they are fitted with liebigs. They are very handy if you can get a deal on one. Most liquids, even low boiling ones like
DCM, condense within the first couple inches of the condenser running suitably cool water. Coil condensers are quite nice but where they really shine
is for loop heat exchange (for example preheating incoming liquid with the condensate to conserve energy in a continuous distillation setup).
Fractionation column: I just use allihn condensers packed with fiberglass weave for fractionating columns. Some of the pictures of my glassware show
this. It is cheap and works well as long as you don't let them get flooded. You can remove the packing to clean it.
IMO the only type of separatory or addition funnel worth a dime is a graduated pressure equalizing one. The non-equalizing funnels are useless for
90% of things.
It is indeed wise to get a wide range of boiling flask sizes, some with multiple necks. Sometimes it is nice to have a vacuum/pressure gauge on one
depending on what you're doing. You'll probably want to have something bigger than 1L, even if you don't intend on doing very large batches. It's
nice to have room for liquids that bubble and foam a lot. IMHO a good range is say from 100mL to 3000mL. Single neck flasks are quite limited, it's
nice to have at least 3. For the larger sizes you should look for a large center neck and just use an adapter to hook it to other stuff, so it's
easier to poke around in and clean. Another thing to look for if you can find one is a reaction kettle with one of those removable tops. They are
great for boiling down solids since most solids cannot be removed from a round bottom flask with small necks.
Hope this helps, and happy experimenting
[Edited on 2-8-2008 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
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DJF90
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It does indeed help. A couple of points to make though that may influence you're advice (and further comments):
- Although 24/40 is the most common size in the US, I am not bothered by availability as I have found a decent supply. 10/19, 14/23, 19/26, 24/29,
29/32 and 34/35 are all readily available, although more so for the 14/19/24 sizes
-A 1L flask is plenty big enough for my liking. Building a heating mantle for anything bigger will be too costly, and so I am happy working on this
kind of scale.
-The pressure equalising funnel is all good. Graduated is not something I can get, but I don't mind. However when dealing with workups, it is
sometimes required to shake the extract with acid/alkali to neutralise something or to perform some other kind of wash. Would the pressure equalising
"arm" not allow the liquids to escape the funnel when shaking/mixing? Hence why I propsed a seperate sep. funnel.
-As for the fractionation column, I should have specified that I would probably need separation down to about 10C difference in BPs (for ethanol
distillation from methylated spirits. Maybe there are other close boiling mixtures I will have to deal with also). Therefore I am leaning towards the
pear bulb column as it looks like it could provide excellent separation, albeit costly
The reason for choosing 19/26 joints is that I want to be able to have a good throughput (for reagents), yet have minimal hold up (for the small scale
experimentation).
[Edited on 3-8-2008 by DJF90]
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starman
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| Quote: |
I just use allihn condensers packed with fiberglass weave for fractionating columns
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Do you mean fiberglass like they use in swimming pools,surfboards etc?If so are you restricted by reactivity/temperature etc?
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kilowatt
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It's fiberglass weave like used for patching boat hulls and such. It is just glass, only in fiber form. I've distilled fuming nitric acid with it
with no damage. It melts at a dull red heat. They also make stuff that is just like randomly tangled up fibers, but that would get wetted over too
easily, reducing effectiveness. With more viscous liquids, the weave would be limited too, and in that case more loosely packed stuff or rachig rings
would be better. For compatible chemicals, stainless steel or copper scrubbers work very well too. Most popular packing material among moonshiners.
These high area packing materials like fiberglass or metal scrubbers actually perform better than rachig rings or balls or vigreux or any of the
ready-made column types.
[Edited on 3-8-2008 by kilowatt]
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woelen
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Running a distillation without watercooling can be done, but then you should NOT use a cooler, which has the tube inside a larger tube (which normally
carries the water). The air between the inner tube and the outer tube then acts as an isolator and there hardly is any cooling.
A simple long pipe of not too thick glass works best. You can buy glass pipes with suitable glass ground joints. I also have succes with using a
vigreux column at the place where one normally would have a liebig cooler. A simple 40 cm vigreux column similar to this is the best:
http://commons.wikimedia.org/wiki/Image:Vigreux_column.jpg
The compound I distilled was acetylacetone (CH3COCH2COCH3) mixed with some grease and other heavy non-volatile carbonstuff. The acetylacetone nicely
distilled and cooled in the vigreux column and no water cooling was needed. The grease remained behind and now I have nice colorless acetylacetone
(acac, used as a ligand in transition metal coordination chemistry).
But beware, this method of distilling without water cooling only works with compounds, which have boiling points well over 100 C and one should not do
this on a very hot summerday.
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DJF90
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Any advice as to choice of joint size? And help with the fractionation column and sep funnel would be most appreciated. Which of the two columns
offers the most separation? Does anyone here have any experience with either type?
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kilowatt
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Haven't all these questions been answered by our discussion? Answering them would be review.
The mind cannot decide the truth; it can only find the truth.
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Klute
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I've always been using 19/26 at works, and have found it to be the ideal size for the scale of reactions I do, between 25 and 250mL reaction mixture
usually, but even recations in 1l and 2L flask (maximum though). I have even a 2L 3-neck RBF with 19/26 and 29/32 central neck that I use
occasioanlly.
I have a few single neck RBf with 29/32 joint (i use an adaptator to attache the distns etup), for removal of solvents, and being able to scrap out
formed solids and such. the only things for which I would like to have a 24/29 or 29/32 setup is for distn of solvents, but I manage very well without
for the moment, just takes more time.
I really advise 19/26 setups for laborator preparative scale.
For the seperating funnel, 24/29 and 29/32 opening are best. I have 100, 250mL, 500mL and 1L, but the one i use the most is the 250 and 500mL. I
fyou ahev to choose only one, I would advise 500mL, a seperating funnel is rarely too big, only too small. Just leave it a few min to let the mixture
on the side to fall down, not much looses. If you realize you have the need for one, you can always get a 250mL after.
I only use vigreux columns, but then I mostly us ehtem whenr emoving solvents from somewhat volatil products. When i distill my solvents, I use a
400mm one, I guess I could get amuch better seperation with another decent column, but don't ahev the need for it considering the price.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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DJF90
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Thats very helpful Klute, thanks. I was worried about losses from using too big of a funnel, but as you are assuring me this is minimal with a little
patience then I think I will go with a 24/29 250ml sep funnel. I think 500ml may be a little too big for my uses, but I shall ponder some more.
@kilowatt: I have gone through every thread relating to this issue in the "reagents and apparatus acquisition" section, and have yet to find the
answers to the questions I am asking. I am nearly 100% sure that 19/26 joints are what I will get, so that issue is pretty much dealt with (unless
someone wants to tell me why I shouldn't get this size? The only alternative would be to get a 14/23 setup AND a 24/29 setup, too expensive for me at
the moment )
The main issue now is the fractionation column. A dufton column may be the best option considering price, but what if that particular pro is removed?
I would not mind shelling out the extra cash for the pear bulb column if it is sufficiently better (in terms of fractionation, thoughput, holdup,
column flooding etc.)
"Images" of the two columns can be found here:
http://www.jindalmedical.com/laboratory-glasswares/Fractiona...
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not_important
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I'm sort of backing up Klute on vigreux columns. They're are simple to use and cheap, it's worth having one or two for less demanding distillations.
Some older lab technique books rated them only slightly below packed columns using solid beads, with much less holdup and flooding problems.
Can't help you on Dufton vs pear-bulb, my good columns are jacked Oldershaws.
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panziandi
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All of my glassware ranges from B10 to B24.
B10 which is on 2x rbf 5mL and 10mL a neck adapter liebig condenser and reciever bend.
B14 I have on 25mL to 100Ll flasks (I don't recomend it on 100mL rbf it's tricky to get inside and clean etc), condensers and additional funnels.
B19 I have on all size flasks from 25mL upwards, condensers and addition funnels.
B24 I have on larger flasks mainly but also smaller ones like 50mL and have suitable adaptors to allow connection to other glassware.
I have larger necks for rotovap etc.
I would recommend either B24 or B19 if you are working with flasks of 100mL upwards also they suit a 50mL flask well too. I'm more a B19 fan myself,
and anyway you can always get adapters to change sizes.
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