Synthesis Reactions in Chemistry: Types and Equipment

A synthesis reaction builds one product from two or more simpler starting materials. Most synthesis reactions chemistry pages stop at the A + B → AB notation. The classes that matter in practice, from direct combination to condensation and polymerisation, differ by heat released, pressure required and phases involved, and each difference decides which reactor you run it in.

What is a synthesis reaction?

A synthesis reaction, also called a combination reaction, joins two or more reactants into a single more complex product. It is the mirror image of a decomposition reaction, where one substance breaks into several. In the shorthand every textbook uses, that is A + B → AB, and if you are sitting an exam, the shorthand is the whole answer.

We build reactors, and we read that arrow differently. Someone sends us a reaction scheme written as one line and asks what equipment runs it. The arrow is the cheapest part of the sentence. It says nothing about how much heat comes out, whether a by-product has to leave the vessel, how thick the mixture gets late in the batch, or whether a reagent arrives as a gas that has to be held above atmospheric pressure. Those four things are what you actually buy hardware for.

So treat the classification below as a hardware classification, not a notation one. Two reactions that look identical on paper can need vessels that share nothing but a stirrer.

What are the main types of synthesis reaction?

Chemists group synthesis reactions into a few standard families. What follows is the same list you will find anywhere, with the column nobody else fills in: what each family demands from the equipment, and which of our reactor specs answers that demand.

Read the last row twice. It is the most common mismatch we see in enquiries: a reaction scheme that quietly assumes hydrogen or nitrogen held above atmospheric pressure, sent to us alongside a request for a glass reactor. Glass is not a compromise choice there. It is the wrong choice.

Why does the reaction type decide the reactor?

Four questions turn a reaction class into a specification. Answer them in order and the vessel mostly picks itself.

How much heat comes out, and how fast? A synthesis that combines two reactants into one product usually releases energy. If the jacket cannot pull that heat out at the rate the reaction makes it, the batch runs away. This is why nearly every synthesis vessel we ship is jacketed, and why the jacket is only half the answer: the circulator or chiller on the other end of those hoses does the work. We cannot tell you the kW you need from a reaction scheme. It depends on your exotherm, your batch size and your hold temperature, and it gets confirmed against the process rather than guessed from the vessel volume.

Does anything need to leave? Condensation reactions expel a small molecule. Either you reflux it back and hold the volume constant, or you strip it out to drive the equilibrium forward. Both need a condenser and a port sized for it. On the BSF-10L that port is KF40, and the matched condenser is a Φ102*L300 coil unit with 12 mm barbed connectors for vacuum and circulation.

How thick does it get? A thin solution wants speed. A polymerising melt wants torque. That trade-off is visible in our own spec sheets: the 1L-3L bench glass reactors spin at 60-1000 r/min on a 40W to 90W direct motor, while the 10 L stainless unit uses a 90W motor with 1/3 gear reduction and tops out at 60-600 rpm. Same motor rating on the larger vessel, lower ceiling speed, more torque at the shaft. That is a deliberate choice, not a downgrade.

Does it need pressure? If yes, stop reading the glass catalogue. Our glass reactors are rated for vacuum or normal pressure, and the SF bench range reaches -0.095MPA on the vacuum side. Positive pressure is a design-pressure question we confirm per application, and it is not something you read off a capacity chart.

Which synthesis work runs in a glass reactor?

Most of it, honestly, at development scale. A jacketed glass reactor covers reaction, crystallization, extraction, distillation and process development in one vessel, which is exactly the mix a synthesis chemist runs through in a week. The body is GG3.3 high borosilicate glass, capacities run from 5L up to 200L, and the working range is -120°C to 300°C when the matched external temperature-control equipment is there to deliver it.

That temperature span is why glass survives in synthesis long after you would expect metal to take over. A cryogenic step and a hot reflux can happen in the same vessel body on the same bench, with the circulator doing the switching. And you can watch the reaction. On an unfamiliar route, seeing the colour change, the precipitate drop and the gas evolve is worth more than any probe you could add.

The trade you accept is pressure and mechanical robustness. If you are weighing that trade seriously, our note on where a stainless steel reactor beats a glass reactor puts the two side by side on the criteria that actually flip the decision.

At the bottom of the range, the bench models are where a new synthesis route usually starts. Here is the real sheet for the 1L to 3L double-layer units:

Two rows deserve attention if you run addition chemistry. The constant-pressure funnel grows from 100ml on the 1L to 250ml on the 3L, and that is the dosing budget for your slow-addition step. The motor jumps from 40W on the SF-1L to 90W on the SF-2L while the speed range stays at 60-1000 r/min, so the extra power buys you the ability to hold that speed in a thicker mixture rather than to spin faster. The full 1L-3L double layer jacketed glass reactor page carries the rest of the sheet, and the larger 5L to 200L systems sit on the jacketed glass reactor page. If you want the whole family in one place, the glass reactor category lists every size and layer configuration we build.

A double layer body is not automatic. You choose it when the vessel needs circulation support from a chiller or a heating circulator, which for synthesis is nearly always. A single-layer vessel is for the mixing and storage jobs where temperature takes care of itself. Our jacketed glass reactor selection guide walks through the layer, port and lifting choices in the order we ask about them on a quotation.

When does glass stop being the right vessel?

Three triggers, and in our experience only three.

The first is pressure, covered above. The second is scale-up shock: a route that behaved at 3L in the fume hood now needs 10 L of working volume in a frame that lives on the floor and gets knocked. The third is a mechanical or thermal duty the glass body is not built for, where you need metal construction with proper stirring and temperature-control connections.

Our BSF-10L answers all three at that first scale-up step. It is a double-layer stainless steel reactor with 10 L capacity. Here is how it lines up against the bench glass range, and below that, the numbers straight off the parameter sheet, not rounded for marketing.

Notice what does not change when you move from glass to steel: the vacuum. Both the SF glass bench range and the BSF-10L reach -0.095 MPa. If you were hoping the metal vessel buys you a pressure regime, the sheet says otherwise, and that is the honest read. What the steel gives you at this size is construction, a floor-standing frame at 740*600*1550 mm, a bottom discharge sitting about 447 mm up so you can put a drum under it, and an LCD controller that reads temperature as well as speed, which the bench glass units do not. One more practical row before you order: 220 V/50 Hz as standard, customizable to 110 V/60 Hz. Confirm your supply before the unit ships, not after it lands. Full detail sits on the BSF-10L double-layer stainless steel reactor page.

How do the lid ports map to the synthesis step?

This is the part of reactor selection that gets skipped and then costs a month. A lid is not a lid. Every port on it corresponds to an operation in your synthesis, and if the operation is not on your list when you order, the port is not there when you need it.

The BSF-10L lid sits on an ID Φ220 mm, OD Φ237 mm flange and carries seven working ports. Here is what each one does in a real run:

Port A is a Φ50 mm flange for the stirrer. Port B is KF25 for the constant-pressure funnel, which is your dosing line on an addition step. Port C is KF40 for reflux and condensation, the port a condensation reaction lives or dies on. Port D is KF25 for a thermometer sleeve 300 mm long, deep enough to read the bulk instead of the wall. Port E is KF25 for the feeding valve. Port F is a Φ50 mm illuminated sight glass, which is how you win back some of the visibility you gave up leaving glass. Port G is KF40 for solid charging, and it is the one people forget until the day they have to tip a few kilos of powder into a sealed vessel.

Count your synthesis steps against that list before you sign anything. Addition needs B. Reflux needs C. A solid reagent needs G. A route with all three needs a lid that has all three, and retrofitting a port into a finished lid is not a small job.

How do you match your synthesis to a reactor?

Four decisions, in this order.

Pressure first. If any step needs positive pressure, the glass ranges are out and we scope the vessel around the design-pressure requirement rather than around the volume.

Then your real working volume, not your hoped-for one. Skip the 10 L if your batch never exceeds 3L. The bench SF range is the right home for a route still in development; the 5L to 200L jacketed glass systems cover the step after that.

Then the temperature profile. If the route stays between -120°C and 300°C and you have the circulator to deliver it, GG3.3 glass handles it and lets you watch. Match the circulator to the exotherm, not to the vessel label.

Then the ports. Walk your scheme step by step and write down the dosing, reflux, thermometer, feeding and solid-charging operations. That list is your lid specification.

When we quote a reactor, we ask for exactly this: volume, layer structure, whether you pull vacuum, the condenser configuration, the feeding method, and what temperature-control equipment you already own. Our equipment selection guide covers the same ground across product families if your route touches distillation or extraction as well.

FAQ

What is a synthesis reaction in chemistry?

A synthesis reaction combines two or more simpler reactants into a single more complex product, written A + B → AB. It is the opposite of a decomposition reaction. The families you meet in practice are direct combination, addition, condensation, polymerisation and the multistep routes used in API manufacturing, and they differ mainly in how much heat they release and what the vessel has to do about it.

What temperature range can a glass reactor handle?

Our jacketed glass reactors are built from GG3.3 high borosilicate glass and cover -120°C to 300°C when suitable external temperature-control equipment is fitted. The vessel does not set that range on its own. The circulator or chiller on the jacket loop delivers it, so the reactor and the temperature-control unit have to be selected together rather than one after the other.

Can a glass reactor run a synthesis under pressure?

Not positive pressure. Our glass reactors are specified for vacuum or normal pressure, with no positive pressure unless specified, and the 1L-3L SF bench range reaches -0.095MPA on the vacuum side. If your route needs a reagent gas held above atmospheric pressure, that is a design-pressure requirement we confirm per application, and it moves you out of the standard glass catalogue.

Why does the 10 L stainless reactor stir slower than a 1L glass reactor?

Because it is geared. The SF-1L runs a 40W motor direct at 60-1000 r/min, while the BSF-10L runs a 90W motor with 1/3 gear reduction at 60-600 rpm. Gear reduction trades top speed for shaft torque, which is what a larger and thicker batch needs. Paired with the two-blade anchor impeller, it is a build aimed at viscous mixtures rather than fast thin ones.

Which reactor suits multistep API synthesis?

Route development almost always starts in a double-layer jacketed glass reactor, because one vessel covers reaction, crystallization, extraction and distillation, and you can see every step. Scale-up moves to a stainless vessel such as the BSF-10L when volume, mechanical duty or metal construction demands it. Both reach -0.095 MPa vacuum, so your workup steps carry across unchanged.

Choosing your configuration

The reaction class tells you what the vessel has to survive; it does not tell you which vessel to buy. Direct combination and addition chemistry at development scale belong in a double-layer glass reactor, where the -120°C to 300°C span and the 60-1000 r/min stirrer cover almost anything the route throws at you. Condensation work needs the reflux port designed in from the start. Viscous and polymerising batches want the geared 60-600 rpm anchor drive on a stainless body. Anything that needs positive pressure is a separate conversation from the beginning. Confirm the volume, the layer structure, the vacuum requirement, the port list and the temperature-control equipment together, and the quotation will match the process the first time. Our equipment FAQ covers the questions that come up most on reactor specification, and we are happy to read your reaction scheme and confirm a configuration against it.