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Texium
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[*] posted on 22-11-2016 at 20:19


Alkyl chloride are less reactive than bromides which are less reactive than iodides. Therefore, chlorides usually give worse yields than bromides and iodides.

Bromides are usually used though because they are less expensive than iodides and give generally good yields. They're also easier to make in most cases. Usually you only see iodides used for methyl and ethyl since methyl bromide and ethyl bromide are gasses while the iodides are liquid and thus much easier to handle.




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[*] posted on 22-11-2016 at 20:41


In the case of aryl halides, aryl iodides are sometimes used when preparing the desired aryl bromide is difficult due to the system being strongly activated towards electrophilic substitution. Iodine is a weaker electrophile, so in some cases iodination can selectively yield a single product, whereas trying to brominate may give polybrominated products.

[Edited on 11-23-2016 by Metacelsus]




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[*] posted on 1-12-2016 at 08:34
just a stupid chem question


this is probably a very dumb question but, is it possible or okay to use a flat normal hotplate/stirrer to heat up a round bottom flask thats held in place with a lab stand? Ive seen it done on youtube a few times and i always thought that it wasnt suppose to be done but in the videos it seems to work just fine.
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[*] posted on 1-12-2016 at 08:43


Yes, that's fine. I do it all the time. Usually the most effective way is to set up the RBF a centimeter or two from the surface of the hotplate and give it a skirt of aluminum foil so that it creates a sort of heated "air bath" between the hotplate and the flask.



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[*] posted on 1-12-2016 at 10:54
App for determinging energy requirements?


I am thinking about a (non chemistry?!) project.

Does anyone use or know of any applications (preferably free) for determining heating requirements vs. ambient air temperatures, R value of insulation, time of year and lattitude/insolation?

Trying to decide if It is worth pursuing a few small projects such as a year round greenhouse and a (solar heated?) duck pond. Total energy required over a heating season, and ballanceing construction material costs against energy costs.

Yes, it's finally looking like winter here...





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[*] posted on 3-12-2016 at 17:10
drying isopropylamine


Just finished distilling a Bach of isopropylamine extracted from a glyphosate herbicide. I want to dry the isopropylamine over a desiccant. Unfortunately, the only desicant I have on hand is anhydrous calcium chloride.

I am unsure if isopropylamine reacts with calcium chloride, is this desicant likely to dry the isopropylamine without reacting with it?

Thanks in advance




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[*] posted on 3-12-2016 at 21:06


Quote: Originally posted by gluon47  
I am unsure if isopropylamine reacts with calcium chloride, is this desicant likely to dry the isopropylamine without reacting with it?
no, you can't use CaCl2 for drying amines,NaOH has to be used
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[*] posted on 3-12-2016 at 21:21


Thanks, I suspected It might react. I might try drying over sodium hydroxide, But doesn't the commercial stuff contain a lot of water? I would have thought this would just make the amine wetter.



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[*] posted on 3-12-2016 at 22:40


Quote: Originally posted by Bert  
I am thinking about a (non chemistry?!) project.

Does anyone use or know of any applications (preferably free) for determining heating requirements vs. ambient air temperatures, R value of insulation, time of year and lattitude/insolation?

Trying to decide if It is worth pursuing a few small projects such as a year round greenhouse and a (solar heated?) duck pond. Total energy required over a heating season, and ballanceing construction material costs against energy costs.

Yes, it's finally looking like winter here...



sorry, not what you wanted but related;
. a small kerosene heater is enough for a typical greenhouse in England
. on a clear winter's night, everything radiates into -270 C black sky and nothing useful comes back,
so blocking the radiation makes a huge difference,
I use wood over, or a thick blanket under, the glass/plastic and it helps a lot.
The sun is so low in winter that most light comes sideways,
so I leave the 'heat shield' on all winter.
I also 'double-glaze' by hanging bubble-wrap inside (one or two years of uv destroys it)
and have Al foil on the North wall.
and when ventilation is not in use, ensure that there are no draughts.
these things add up to massive heat savings.

Here, for p.v. solar cell calculations, daily insolation is c 500 W.h/m2 mid-winter - when you actually need it.
(summer c 5 kW.h/m2)

IF possible, using the existing wall of a heated building as one wall of your construction both scavenges heat and insulates the wall.

good luck with the solar heated duck pond - sounds quackers to me !
EDIT: duck pond afterthoughts;
. a mirror would be more efficient than a p.v. panel
. due to freezing, direct solar heating of water is risky, so bio-unfriendly liquids in heat exchangers need to be avoided.

sorry for veering of towards whimsy.

[Edited on 4-12-2016 by Sulaiman]




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[*] posted on 4-12-2016 at 21:29


Ok, I went ahead and dried the isopropylamine over NaOH. The amine looks like it has taken on a slight cloudy tinge and I'm wondering If there is enough water present for some of the sodium hydroxide to dissolve.

Can I simply decant the amine off and have no NaOH contamination or Is it necessary to distill the amine after drying to remove NaOH?

[Edited on 5-12-2016 by gluon47]




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[*] posted on 8-12-2016 at 14:12
Heating Mantle question


Ive noticed on ebay that there are heating mantle/stirrers that go from sizes for 100ml round bottom flasks up to 250, 500, 1000, 2000ml.

My question is, if i get a heating mantle/stirrer for the 2000ml round bottom, would i also be able to use that for smaller round bottom flasks or would i have to get the exact size heating mantle for each different size flask?
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[*] posted on 8-12-2016 at 14:17


If you mean something like this:
http://www.ebay.com/itm/220V-2000ml-2-Litre-Lab-Electric-Hea...

Then I would guess not, it looks like the mantle is formed to fit a specific size.
I could be wrong though.
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[*] posted on 8-12-2016 at 15:24


I have, in the past used heating mantles larger than the size of the flask I was using. Except for gentle heating I would not recommend it. If you attempt to drape insulation around the flask and the mantle to hold in the heat, do not forget that air is a poor conductor of heat. In the times when I have done this I have inadvertently 'glassed' the mantle. In other words it glowed red hot and the glass wool body of it stopped being flexible and became a brittle mass.



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[*] posted on 8-12-2016 at 15:28


oh thats a shame, thats going to be quite expensive then getting 2 or 3 heating mantles.
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[*] posted on 8-12-2016 at 15:41


Just get one for the size of flask you think you'll use the most and use a hot plate with "air bath" for everything else. I've gotten by just fine the last few years without a mantle at all, though I wouldn't mind having a 500 mL one.



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[*] posted on 13-12-2016 at 07:53
need to know where to buy 2 basic things


first i need to know, can anyone give me a link or tell me a place that sells a filter flask side-arm stopper? i need something that can be put on the end of the side-arm of a filter flask to close off that hole. Any ideas? i cant find a name or anything fo rwhat this would be called.

Also can someone link me to a site that sells a good vacuum tubing for vacuum distillation?
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[*] posted on 13-12-2016 at 08:58


I don't understand why you would need to close off the side-arm of a filter flask. I can think of quite literally no situation where that would be necessary. Such an item does not exist.

As for tubing, you can buy it at hardware stores in bulk. Just get a kind that isn't too flimsy and it should be sufficient.




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[*] posted on 13-12-2016 at 11:23


Quote: Originally posted by zts16  
I don't understand why you would need to close off the side-arm of a filter flask. I can think of quite literally no situation where that would be necessary. Such an item does not exist.


A rubber pasteur pipette bulb will work.




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[*] posted on 15-12-2016 at 00:27


Can i turn an amino acid into an amide rather easily by any chance? Im looking for the best method of converting the Amine in the amino acid into an electron Withdrawing group. Any suggestions. There is Oxidation i believe to convert it to a Nitro compound but from what i understand this is finicky and Its better if i have something reversible with relative ease.

IDK Suggestions anyone.





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[*] posted on 24-12-2016 at 08:40
Question


1. Does a 24/29 joint fit in 24/40 joint?
2. Is it possible for an individual person to order chemicals from big companies like alfa aesar ect.
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[*] posted on 24-12-2016 at 09:32


1. Short answer: yes. Long answer: In the vast majority of cases, there won't be any issue since the joints are compatible. However, the two may not fit together when you have a male 24/40 joint and a female 24/29 joint, and there is a rapid bend or constriction near the 24/29 joint. Since a 24/40 joint is longer than a 24/29 joint, it needs some room to extend past the end of the joint, which it doesn't have if there is a constriction.

An examples is certain types of 105° vacuum takeoff adapters, which is the most common place I've heard of an issue.

2. There has been extended discussion about this topic on the forums. While there is some variation in policy between the different companies, none of them are interested in selling anything to individuals; they will tell you that flat out if you ask them. Second tier suppliers such as Carolina Biological will sell certain things to individuals(IIRC only equipment, no chems).

If you need a certain chemical from Sigma Aldrich or Alfa, try contacting Elemental Scientific. For a while, they have been running a Special Order program, where they will order a chemical from one of the big suppliers, then ship it to you for a slight fee. That's going to be your best bet at sourcing something if it truly is unavailable everywhere else.




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[*] posted on 25-12-2016 at 15:45


Quote: Originally posted by Sedit  
Can i turn an amino acid into an amide rather easily by any chance? Im looking for the best method of converting the Amine in the amino acid into an electron Withdrawing group. Any suggestions. There is Oxidation i believe to convert it to a Nitro compound but from what i understand this is finicky and Its better if i have something reversible with relative ease.

IDK Suggestions anyone.

There are many ways but it is better to know what you intend to do and the initial starting molecule...otherwise answer may be too general and vague for your specific application.

To increase the EWG power of an amine, you have to reduce its basicity...

Oxydation of the amine to nitroso or nitro may help decarboxylation of the alfa carboxylic acid group (spontaneous for nitroacetic acid).
If H is available into alfa position then the nitroso can be seen as C=N-OH

If you turn your amine into amide with an organic acid anhydride or organic acid halide, it will be more EWG.

If you add formaldehyde to it also because of CH2=N- or (HOCH2)2N-.

Halogenation of amino-acids provides haloamines that may decarboxylate and on further treatment turn into ketons or nitriles...all depends onto the struture of the carbon holding the NH2 (primary, secondary, ternary)...

Nitrosation may afword diazo-carboxylic acids which display very special chemistry see diazoacetic esters from glycine esters.

[Edited on 26-12-2016 by PHILOU Zrealone]




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[*] posted on 26-12-2016 at 15:22
Question


Is there a material that is resistant to high temperatures (like 300C) and HF and H2SO4? I can only find things like fluorinated polymers and such. Can't use glass obviously and I don't know of any refractory compositions or metals that HF doesn't react with so if anyone knows of such a tough material please do tell. Thanks in advance!
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[*] posted on 26-12-2016 at 19:42


Tantalum is great for H2SO4, even boiling hot, but it is dissolved by HF, quartz also is immune to H2SO4 and heat, but will be etched by HF. Solid Teflon might be the only thing that will handle that well, I know it handles hot H2SO4 well, as those three materials were all used by IBM years ago to hold silicon wafers to be cleaned by immersing them in to boiling sulfuric acid. That would dissolve any fingerprints, hair, dust, fingers, and any other dirt on the wafers, they came out sparkling clean. That was one of the most hazardous places in IBM.

Teflon is actually not that hard to work with or machine, so if it is strong enough, you could test it for your work, although at high temperatures, it gets softer, so it may need to be held in some other material for support.
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[*] posted on 28-12-2016 at 04:47
viton O rings


If I wanted to purchase some replacement O rings for thermometer adapters (normal 6mm diameter thermometer) what size should I get? I have now idea how these things are measured.



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